User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-96.91.247.202-20150930204951/@comment-3045936-20150930212144

Well, as in one of the books. In heaven there was a god named Ovlivion. It was to erase the memories of supernatural things from people. But maybe after most of those entities die they aren't supernatural anymore, and appear human biologically.