There is no way to ban only the bad use of AI, especially since nobody agrees on where the dividing line between “good use of AI” and “bad use of AI” is. Open the door to AI at all and everybody gets buried under an avalanche of slop, true creators and “but I only use it in acceptable ways” AI apologists alike.
Of course, itch.io was a slop heap even before generative AI was a thing, so it’s not surprising that nobody is doing anything about this.