Twitter will probably follow suit as soon as their investors change up on them...same thing happened to Tumblr and Facebook.
Its hard for unverified content, you have no idea if the person is a minor. Especially a lot of these hardcore porn videos have other people in it, its a tricky slope and governments ain't playing around anymore
Pardon me if i'm wrong but to use onlyfans i think you just have to show photo id, but if you say shoot a video with someone else (hardcore porn) there is no verification for that person. So a guy like r kelly could show id and he's of age but he shoots a video with some 15 year old girl and there is no way for only fans to confirm that persons age.