The goal of most platforms is to get more adoption and more users. People who post hateful, weird, and/or borderline illegal content are mutually exclusive with the vast majority of other "normal" people. When the majority of people view something as tainting then the platform will remove it because hosting it will taint the platform and the majority of people will leave the platform, or not join it in the first place.

Remember Voat. They wanted to be "free speech Reddit" but predictably they turned into a cesspool of degenerate users, even for a time hosting the r/jailbait folks who had been kicked off Reddit a long time ago. And unsurprisingly Voat never got mainstream and now it is dead, while Reddit is still online and growing more and more all the time.

It isn't "censorship". It is optimization.