It's a version of the library of babel filtered only to the books which plausibly consist of prose. The set is still incomprehensibly vast, and all the more treacherous for generally being "readable".

“Biased” more than “filtered”; LLMs, though its harder with the better ones, can, when prompted “right” (or “wrong”, depending on your perspective), produce output that is not plausible prose, though obviously they are crafted to respond to the expected style of prompting with things that are plausible prose.