you said: To ban (generative) AI, it would have to be illegal to begin with.
Not at all. This is a private site. You're subject to whatever rules the powers that be decide to make. Your participation isn't mandatory, so you opt to either a) follow the rules or b) not use the site or its services. You may not agree with the rules, but you still have to follow them in order to post here (or any site that's privately owned).
Also, re: legality -- For visual art (and probably writing, though I haven't seen any cases on it yet), you already can't copyright AI-generated content. It's technically not yours. It's still new enough that the legal rights/status of content created by machine is still being debated (obviously), but right now, if you put up a game with AI images, and some other creator came along and used all of your images with their own text? It's legal. It's shitty. But it's legal. (And no shittier than stealing from a bunch of artists by using AI, really.)
I buy a lot of games here. I want to know my money isn't going to lazy AI-bros. From the perspective of someone giving y'all money, I'd much rather give a human money than reward unethical gen-AI prompt typists.