Teenagers aren't running generative models on their home PCs, they're using online tools. Sure, some people will do it offline, but these are by and large crimes of opportunity.
Horny Teenagers Find A Way. If the online tools were all magically shut down today, by tomorrow, they'd all be running local models on the local computer nerd's gaming GPU rig.
I doubt it. Photoshop was already pretty accessible, moreso than downloading sketchy models and getting them to run.
It's also a matter of scale. If a dozen teenage boys in a class are generating nudes, they feel safety in numbers. If it's only the weird computer kid who can do it, it's far easier to address and far more likely that it'll blow back on him.