Appreciate how good you have it. In America, child sex abuse material is only illegal when children were abused in making it, or if it’s considered obscene by a community. If someone edits adult actors to look like children as they perform sex acts, it’s not illegal under federal law. If someone generates child nudity using ai models trained on nude adults and only clothed kids, it’s not illegal at the national level.
Fake porn of real people could be banned for being obscene, usually at a local level, but almost any porn could be banned by lawmakers this way. Harmless stuff like gay or trans porn could be banned by bigoted lawmakers, because obscenity is a fairly subjective mechanism. However, because of our near absolute freedom of speech, obscenity is basically all we have to regulate malicious porn.
I guess because people still use it. It might be obvious, but it isn’t common knowledge. All people are ignorant about most things. There’s just too much to know and not enough time to learn it unless you’re forced.