Re: Why some things are missing from Quran ?
I heard that Hazrat Abu Bakr (I need to confirm that) burnt his compilation of 3000 hadees for the same reason that you mentioned (he was afraid that what if by mistake he passes a flawed version of the Hadees as that would be a huge disservice to Islam) - but also shows that hadees were compiled during prophet’s time, just not in a book form.