Why are you on a platform open to accepting them in the first place?
Are we talking about the same thing?
Git hosting provides discoverability and the ability to fork repositories. Everything else is an optional feature.
because you don’t have to “drive a hard line”, to do that,
you just draw it once (publish a no PR policy, don’t host on GH, etc),
and you shouldn’t be hearing from users.
So, reviewing them.
Which takes time/focus.