I personally believe it's dependent on the audience/player-base of each individual game jam and the niche its meant for, not so much that jams or hosts themselves are anti-AI (although some are. Again, it depends). The ones who are restricting AI usage are probably doing it to retain their current player-base.
How do I explain this..... I come from the narrative game niche, moreso the VN niche (it's a pretty large one here), so I will speak from my experience with this niche. From what I know, a lot of VN players/readers are vehemently against AI, unless you're from the hentai/porn demographic, which seems to currently be split in half.
That's right. Even porn consumers are arguing over AI.
Anyway, a lot of VN players join and bookmark Game Jams to view and play the games there. My first VN got a heap of organic players - you're talking hundreds here - all because I'd submitted it to a very popular VN jam, so I know there are a lot of organic players browsing them to play games. Sometimes I still get referrers from older games from the old jams I had joined. People still browse them for something to play.
This pool of players is what the game jam hosts are probably trying to protect. If they allowed AI into the game jam, the player-base will more than likely flip out and leave. And in an indie game environment, organic players are everything, so it's understandable that nobody wants to risk losing them.
I remember an account from this guy who used AI to "correct" a few of the monster render asset art pieces he had commissioned from different artists, to make the monsters in the story look more streamlined. One or two of the players noticed the look and commented about it. It caught fire and a LOT of his players either commented or DMed him to ask. He admitted it, I think he made a new post about it or something after a few days.
Hell broke loose. Like, dude lost 80% of his player-base in two weeks or so because his (now-ex) players were posting about it on socmed, Discord, etc. His Patreon supporters dropped until it was just a handful left. Within two months, he shut his personal studio down. He had actually invested money in it and... now it's just gone.
I think a lot of Game Jam hosts are scared that this will happen to them too, especially the very established ones, so they may have banned AI as a result. A lot of players are starting to pay attention and try to spot AI, and they do have demands that need to be met. These players use Game Jams to effectively filter out AI games as a whole, since the hosts will check and remove AI games when found, because a lot of bad faith actors have been purposely tagging their AI games as No-AI. I've seen comments by players attacking AI devs in their comments for tagging their AI games as No-AI, and I feel that this is just the tip of the iceberg.
Too many bad faith actors have appeared and given AI games a bad name, refusing to respect and follow rules and etiquette. They are also why game jams have started banning AI.
If it helps, you can still do whatever you like and make your AI games and make your dreams come true. Nobody can stop you. Nobody is allowed to attack you for it. But bear in mind that you are not worth losing subscribed players over. In the indie environment, players are worth more than we developers.
I'm currently experimenting with AI to code an upcoming game and being very upfront about it, but I would never, EVER try to submit it into any jam that doesn't allow it, because I believe their rules and demands of their player-base need to be respected, nor would I complain about it because I can understand where they're coming from.
You can submit your games to AI game jams, or like the other user said, host one yourself. Try not to be entitled to other people's jams.