That's a broad statement that's untrue for most genres, at least right now. However, it is true for the YA lit / chic-lit and the smut-disguised-as-fantasy genres. These already have authors pumping out a book every few months with different characters jammed into similar situations. And people have personalized these kinds of interactions already (CharacterAI and others). Literature is literature, whether human or LLM-generated and will sell like hot cakes if it caters to the common denominator well enough.

It can also be seen in newer fanfics. If you visit AO3 you might get to see a few that are completely written with LLMs and the authors sometimes don't even bother reading it themselves before publishing it. The lower quality is almost always apparent from the get-go.

LLMs can be very useful for writing, but I don't see serious writers using LLMs except for maybe checking facts / as a knowledgebase. The lowest tier of readers was already one-shot by LLMs over a year ago.