Ramadan: Why do sunnis think imam Bukhari is infallible?

No he is not infallible, you see not all the hadiths are authentic because you have people like Bukhari and others who started recording hadiths after three hundred and something years after the prophet saw death. Think about it, how many generations have passed during the period and ofcourse the longer it is the less accurate the hadiths are which becomes like chinese whispers if get what I'm trying to say, so this is why some of the hadiths are weak and not all are reliable.