The Bible isn’t just a book, it’s been a massive part of human culture for millennia, to the point of it shaping language itself. LLMs might be able to memorise the Bible, but it’s not because they can memorise books, it’s because the Bible is far more than just a book.
I doubt every part of those books get quoted everywhere on a numbered basis like the bible might be. For only recently public domain books it seems to be overly cautious trough the retroactively applied filtering where it refuses if it suspects there might be a single country where copyright still applies.