I believe the thing with FNAF porn, or Minecraft porn, or porn of most shows and games mostly aimed at/associated with children is that you have young people discovering their sexuality while they're also into said show or game, so those wires end up getting crossed and when they get a bit older they start making/consuming porn based on characters they liked.

It would make sense for some weird teenager on 4chan to be cranking it to FNAF porn (editor's note: not really ) but for Jeffrey Epstein, an incredibly rich guy in his 50s to even know what that is is fucking mind-bending