because you’re paying

Well no, it’s the buyer who is paying. Which they might find off-putting, if the final price is too high, so you get fewer buyers and less profit.

As for the quality, there’s literally no reason that a book that is printed on demand has to be low quality or use low quality materials.

Except that in practice they simply are of lower quality. I’ve seen quite enough of such books. Maybe higher quality materials could be used, but that would raise the price for the end-user even more, and possibly slow down the production.

and the proof is the fact that Amazon is filled with AI generated garbage books

One has to wonder how much money they actually make, though. I saw some YT videos about the topic, IIRC it’s really difficult. Their mere presence doesn’t prove their profitability but only the belief by many people that they could be profitable.

It’s easy to start a business, sure. But you didn’t explain the rest of the process and don’t seem to actually know a lot about the particulars of book publishing (neither do I, but whatever I do know doesn’t agree with your imagined “solution”).