But then you need to factor in that the rights holders would need to agree to that. AI companies don't get to simply decide what peoples work is worth, they need a licensing agreement. (Otherwise they need to successfully argue that what they're doing is fair use.)
And when you add it up and realize that "AI" is a black box based off a training dataset of thousands (if not millions) of pieces of copyrighted artwork, all the sudden you start to see the profit margins on your magical art machine (POOF!) disappear. Oh, won't someone think about the tech venture capitalists?!