In the US, CSAM bans are on slightly shakier ground than in other countries because of the First Amendment (and the general trend in law over the past 100-ish years of liberalization of interpretations of 1A... pornography bans were rolled back significantly by various lawsuits around
Hustler and its owner). They're grounded, more or less, in the notion that their creation is itself always a criminal exploitation of a minor, so trading in them is always encouragement of criminal creation of more such material (essentially, the idea that 1A doesn't apply because one is creating a marketplace for goods that are illegal to create).
This argument falls flat regarding synthetically-produced CSAM and CSAM-adjacent material (no human beings exploited in its creation; in fact, one could argue that creation of synthetic CSAM depresses the market for child-exploiting CSAM), so I wouldn't be surprised if the US can't find a way in their legal structure to ban such material; their protections against obscenity in general tend to be weaker than other nations, and if the content is merely obscene and not generated by harming a minor, it's harder to argue it should be banned (as opposed to shunned for being odious).