Because TikTok isn't a nightclub, it's a place for people to put their own content out on the Internet. Not just people, but primarily people living in a pathologically authoritarian state that doesn't allow them to access other places on the Internet that they could put their content on.

But even ignoring the authoritarian state angle, surely you'd think it'd be weird and counterproductive for user content from YouTube or Instagram or imgur to have similar policies? Those sites are also not nightclubs or modeling agencies or a Hooters franchise either.

FWIW it's totally shitty for nightclubs to be discriminatory in that way. I get why they do it, but it doesn't make it any less shitty of them, and it sure as hell doesn't let them off the hook for their shittiness in this regard.

Tangentially, this is one of infinitely many reasons that nearly all of humanity hates nightclubs, including the people that feel socially obligated to go to them, and including people still young enough to convince themselves that they must be having fun there because it sure looks like everyone else is, not realizing that everyone else is thinking the exact same thing.