This shows that not only are you totally unaware of history, but also are extremely deficient in Usul Fiqh, Dirayah and hadith. You should know that most of the hadiths of the Sunnis were gathered and compiled after the Umayyid dynasty. The Umayyid dynasty ended and it was only after that, that Bukhari (256 ah), Imam Malek (150 ah) and others appeared and this is the reason why most hadith sources were compiled and written during the Abbasid dynasty’s rule, who had taken power with the slogan of supporting the ‘Ahlul-Bayt’.
According to reports in history that can't be denied, the transcription of hadiths was banned by Umar, and since there was no written proof around and also, because there were more than enough motives for the heads of the Umayyids to forge hadiths on false virtues, not to mention all the necessary resources and wealth that was at their disposal and they used for this task, the forging of hadiths became quite common then, and subsequently, the sources that were later compiled (after the writing of hadiths was made legal once again) were based on these same forged hadiths. As for the Abbasid rulers, although they began with the slogan of supporting the Ahlul-Bayt and took power with it, but as time passed, they followed the footsteps of the Umayyids, because it was only by this that they could maintain their rule, or else they would have to hand it over to the Ahlul-Bayt and their followers. Some scholars even believe that the aggression and transgression of the Abbasids was more than the Umayyids.
Paying attention to several points can clear up the answer to this question:
1- The transcription of hadith was banned by Umar  and since there was no written proof around and also, because there were more than enough motives for the heads of the Umayyids to forge hadiths on false virtues, not to mention all the necessary resources and wealth that was at their disposal and they used for this task, the forging of hadiths was quite common then, and subsequently, the sources that were later compiled (after the writing of hadiths was made legal) were based on these same forged hadiths.
Ibn Abil-Hadid narrates from Abul-Hasan Ali ibn Muhammad ibn Abu Seyf Mada’ini  in his book of Al-Ahdath that after the year in which Imam Hasan gave up going to battle with Muawiyah (Aamul-Jama’ah 41 ah), Muawiyah wrote a letter to his governors saying that he has no responsibility towards anyone who says anything about the virtues of Imam Ali (as) and the Ahlul-Bayt. Abil-Hadid also says: He asked the province governors to gather the people so that they narrate hadiths about the qualities of Uthman, the Sahabah and the first three khalifahs and to also counter any hadiths mentioned about the virtues of Ali (as) with the opposite in praise of the Sahabah. Muawiyah’s letter was read for the people, money was spent for this purpose and many forged hadiths about their virtues were narrated here and there and were widely taught to the people’s children and they engaged in learning and memorizing them the same way they would learn the Quran. Jurists, judges, and governors all endorsed this policy and continued it. During this time, the Qaris (reciters) of the Quran were in worst shape, they would display asceticism and humility, but would forge hadiths to draw the attention of the governors and gain wealth in the process. When the reciters of the Quran did this, the trust of the devout believers was gained (because of the important status the reciters of the Quran had then; they were trusted by all) and even they began accepting and narrating these forged hadiths. Abil-Hadid goes on to say: Ibn Arafah, known as Naftawiyyah  , which is a great hadith scholar, has narrated things like this report in his history book. 
Through this strategy, many of Imam Ali’s (as) virtues were wrongfully concealed, although a portion of it remained untouched by the enemy, who wasn’t able to keep it away from the nation; this is a blessing from Allah (swt) and special attention that He gave to the preservation of Islam. What informs us of this concealment of Imam Ali’s virtues is what Abu Ishaq has narrated: “A man asked Bara’ – while I could hear what they were saying – : Was Ali present in the battle of Badr? He replied: “It is clear and obvious.” 
Do you think that Imam Ali’s status in Badr was unknown and unclear in the advent of Islam to the extent that it needed to be asked about?! This is while the victory of the battle of Badr laid on the shoulders of Imam Ali (as) and if it wasn’t for his sword, the Muslims would have definitely lost the battle. This shows to what extent the people then had strived to cover Imam Ali's (as) virtues and accomplishments, and even if they ever did narrate anything about him, they would do it incompletely and deficiently. 
Take this incident for instance: Muawiyah gave four hundred thousand dirhams from the Beytul-Mal (the nation’s treasury) to Samurah Ibn Jundub to speak among the people of Sham and to say that the verse “وَ مِنَ النَّاسِ مَنْ یُعْجِبُکَ قَوْلُهُ فِی الْحَیاةِ الدُّنْیا وَ یُشْهِدُ اللَّهَ عَلى ما فِی قَلْبِهِ وَ هُوَ أَلَدُّ الْخِصامِ وَ إِذا تَوَلَّى سَعى فِی الْأَرْضِ لِیُفْسِدَ فِیها وَ یُهْلِکَ الْحَرْثَ وَ النَّسْلَ وَ اللَّهُ لا یُحِبُّ الْفَسادَ”  (Among the people is he whose talk about worldly life impresses you, and he holds Allah witness to what is in his heart, though he is the staunchest of enemies. And if he were to wield authority, he would try to cause corruption in the land, and to ruin the crop and the stock, and Allah does not like corruption) was revealed about Ali ib Abi Taleb, and to also say that the verse “وَ مِنَ النَّاسِ مَنْ یَشْرِی نَفْسَهُ ابْتِغاءَ مَرْضاتِ اللَّهِ”  (And among the people is he who sells his soul seeking the pleasure of Allah, and Allah is most kind to His servants) was revealed about the wretched of all people, Ibn Muljam. 
It is also good to draw your attention to two books of Mahmoud Abu Riyah  , one of the top Sunni scholars in
Al-Azhar University and ask you to closely study them. In his book of “Adwa’un alal-Sunnatil-Muhammadiyyah” (اضواء علی السنة المحمدیة), he writes:
Scholars all agree that hadith forgery began towards the end of Uthman’s rule, and in order to justify taking away the caliphate from Ali (as), forgery reached its highest during the Umayyid period.” 
For further information on those who fabricated hadiths, see: The Personality of Abu Hurayrah from the Perspective of the Sahabah, Question 969 (website: 1044).
2- Although the Abbasids took power with the slogan of supporting the Ahlul-Bayt, but as time passed, they followed the footsteps of the Umayyids, because if they were not to do so, they would have no choice but to hand over the power to the imams and their followers. Some scholars even believe that their transgression exceeded that of the Umayyids. 
In closing, it should be mentioned that in the tenth volume of his book, Al-Ghadir, Allamah Amini (rah) has a comprehensive and interesting investigation about hadith and fabricated hadiths and has listed around seven hundred narrators who were liars and forgers of hadith, pointing to about half a million  hadiths narrated from forty three of them alone. He also narrates around a hundred false hadiths in which not only the caliphate and virtues of the first three khalifahs are confirmed, but Mu’awiyah, Yazid and Mansur Davaneqi and other Umayyid and Abbasid rulers have all been deeply praised in!!! 
1) The biography of Bukhari and criticism of Al-Jame’ Al-Sahih (Sahih Bukhari), Question 623 (website: 681).
2) The Sunnis and Hadiths Fabricated in Praise of their Virtues, Question 2928 (website: 3186).
 The details of this incident can be studied in Al-Ghadir, vol. 6, pp. 417-428 by Allamah Amini, or in the Farsi translation of Al-Ghadir, vol. 12, pp. 192-208. See: The Nurul-Wilayah software of the Computer Research Center of Islamic Sciences.
 قال الذهبی بترجمته: «المدائنی، العلّامة الحافظ الصادق أبو الحسن علی بن محمّد بن عبد اللّه بن أبی سیف المدائنی الأخباری، نزل بغداد، و صنّف التصانیف، و کان عجبا فی معرفة السیر و المغازی و الأنساب و أیام العرب، مصدّقا فیما ینقله، عالی الإسناد ... و کان عالما بالفتوح و المغازی و الشعر صدوقا فی ذلک» توفی سنة 224، 225 . سیر أعلام النبلاء 10/400 . ترجمته فی: فی: تاریخ بغداد 12/54، مرآة الجنان 2/83، معجم الأدباء 14/124، الکامل فی التاریخ 6/516 و غیرها
 ترجم له الذهبی و قال: «نفطویه الإمام الحافظ النحوی العلّامة الأخباری أبو عبد اللّه إبراهیم بن محمّد بن عرفة بن سلیمان، العتکی الازدی الواسطی، المشهور بنفطویه، صاحب التصانیف ... و کان ذا سنّة و دین و فتوّة و مروّة، و حسن خلق، و کیس، مات سنة 323» سیر أعلام النبلاء 15/75. و توجد ترجمته أیضا فی: تاریخ بغداد 6/159، وفیات الأعیان 1/47، المنتظم 6/277، الوافی بالوفیات 6/130، معجم الأدباء 1/254، و غیرها
 Sharh Nahjil-Balaghah Ibn Abil-Hadid, vol. 11, pg. 44, The Manhaj Al-Nur software of the Computer Research Center of Islamic Sciences; The translation of Al-Ghadir fil-Kitabi wal-Sunnati wal-Adab, vol. 21, pp. 43-46; Abaqatul-Anwar fi Imamatil-A’immatil-At’har, vol. 12, pg.24, The Nur Al-Wilayah software.
 Sahih Bukhari, vol. 3, the book of battles, the chapter on the killing of Abu Jahl.
 Translation of Dala’ilul-Sidq, vol. 1, pp. 5-6.
 Sharh Nahjil-Balaghah Ibn Abil-Hadid, vol. 4, pg. 72.
 Titles: “Sheikh Al-Mudirah Abu Hurayrah”, “Adwa’un alal-Sunnah Al-Muhammadiyyah” ("شیخ المضیرة ابوهریرة" and"َاضواء علی السنة المحمدیة" ).
 Adwa’un alal-Sunnah Al-Muhammadiyyah, pp. 118-119 and 126-135. Imam Muhammad Abduh, in his book on tawhid “Theology of unity”, pp. 7 and 8, stresses on this same point.
 In this regard, Allamah Mir Hamed Hosein (rah) says: “و لم یزل الأمر على ذلک سائر خلافة بنی أمیّة حتى جاءت الخلافة العباسیة، فکانت أدهى و أمرّ و أضرى و أضرّ، و ما لقیه أهل البیت علیهم السّلام و شیعتهم من دولتهم أعظم ممّا مضوا به فی الخلافة الامویة کما قیل: و اللّه ما فعلت أمیّة فیهم معشار ما فعلت بنو العباس ثمّ شبّ الزمان و هرم، و الشأن مضطرب و الشنآن مضطرم، و الدهر لا یزداد إلّا عبوسا، و الأیام لا تبدی لأهل الحق إلّا بؤسا، و لا معقل للشیعة من هذه الخطّة الشنیعة فی أکثر الأعصار و معظم الأمصار إلّا الانزواء فی زوایا التقیّة، و الانطواء على الصبر بهذه البلیة ”. See: Al-Darajat Al-Rafi’ah fi Tabaqat Al-Shia, pp. 5-8; Abaqat Al-Anwar fi Imamat Al-A’immah Al-Athar, vol. 12, pg. 24; Nafahat Al-Azhar fi Kholasat Abaqat Al-Anwar, vol. 15, pp. 42-45.
 Of course, this shouldn’t be very strange, because in the introduction of the book “Fath Al-Bari”, Ibn Hajar says: “Aba Ali Ghasani narrates from Bukhari that he said: “I have selected this collection from six hundred thousand hadiths”, while we know that the number of hadiths (not counting repeats) in Sahih Bukhari don’t exceed 2,761.
 Translation of Al-Ghadir fi Al-Kitab wa Al-Sunnah wa Al-Adab, vol. 10, pg. 8.