I merely mentioned that the Parent knew the name Picasso. I do not assume that the Parent actually knows anything worthwhile about Picasso other than he's a great painter. That means that Parent either has no information to give or gives the wrong information.
Actually libraries were invented to disseminate knowledge and preserve books for very few people. No one thought that the masses should have access.
Again, those civilizations are studied through written records and not verbal ones. Besides the obvious reason why we don't have written records, I doubt they would be useful. Even those burial traditions were written down, even if on caves. Words on papers do not have feelings or opinions, but facts.
Because the only valuable books are the ones that simply describe things and not the ones that give opinions, which is why a history textbook is a million times better than all those opinion pieces on the Daily Prophet.