When slop floods the library faster than it can expand, who will want to maintain that. I don't think we have good enough sorting and rating (or good enough AI output detection) to prevent bookspam.
This is a point in history where "record everything" stops being viable, and we have to start hand-picking the text we want to survive. Indiscriminate things like Internet Archives stop being viable.
Why keep books, anyways? You can just ask the AI to re-generate whatever it is you want to read about on the fly.