AI has made creating content almost free. What it hasn't done is add free hours to our day to consume all this new content. The number of people who want to read a book this month is roughly what it was five years ago, and roughly what it'll be five years from now.
Supply is exploding into demand that is stagnant (at best) or falling. Upload a book to Amazon today — good cover, sharp title, a blurb you sweated over for a week — and there is no longer any reasonable expectation of an organic sale. The book goes up, and then nothing happens, indefinitely.
Five years ago that wasn't true.
The answer is paid advertising. Buy your way onto the shelf. Stand out from the slop. But every writer is being given the same advice at the same moment, and there are only so many slots. The price of the slots must rise. And will keep rising for as long as there are writers able to pay.
The old metric was it takes about $5 to sell a book via paid advertising. I think in a year we'll look back on that figure fondly.