If that wasn't a thing, then they'd end up with even more legal issues than before.
This is actually an established thing w/ FNaF fangames, as a while back there was a fan remake of FNaF 3 that Scott Cawthon asked to be taken down due to it basically being a free version of the original game, to the point where it could technically be considered piracy.
TL;DR, further fan remakes like this are always gonna have to have checks in place to ensure that you own the original game.