> I don't get the point of banning specific pornography niches/fetishes that are otherwise legal.

A typical practice for dictatorships to create a legal system capable of exerting pressure on any opponent.

> Are there not much more objectionable fetishes than this one?

The goal isn't to combat sexual perversions, but to silence anyone the dictatorial regime deems necessary.

You pass a law that's clearly unimplementable, and therefore won't cause much outrage, and then, as expected, the law doesn't work. But when you need to silence someone, a complaint emerges that someone accessed and distributed illegal content (some anonymous on some forum saw their IP-address doing that). In the public consciousness, the violation isn't serious (the law isn't actually implemented), so there's no significant outrage. Meanwhile, you conduct searches of the victim's home, confiscate their computers, laptops, smartphones and other gadgets, and open a criminal case against them.

And then you simply close the case, saying, "Yeah, nothing illegal was found, we are sorry". And the victim (and others) will think twice before going against the dictatorial regime next time. Typical practice, all dictatorships do it