1- Bukhari and Muslim weren’t the ones who transmitted the Quar’an for us.
2- The narrators of Bukhari and Muslim also weren’t the ones who transmitted the Qur’an.
3- The Qur’an was so widely know and memorized by thousands of companions such that it was preserved.
4- Hadith is not like that. Many people didn’t memorize the hadith like they memorized the Qur’an. Also remember that the caliphs banned the recording of Hadith for nearly 100 years after the Prophet (s). Hence many hadiths got fabricated or changed. Bukhari was compiled some 200 years after the Prophet (s). How can we trust that all those hadiths were preserved and remained intact all that time?
5- There are many distubring hadiths in Bukhari that clearly indicate they were fabricated.