The word or phrase “law library” used to mean “the place to get the law”. Before online databases, there wasn’t any other place to get the law – it was too big to put in your pocket or sit in your office. Even law firms with a few shelves of books called it their “law library”.
“Law librarians” were the people who knew where to find the law and how it interrelated. Law is certainly not self-organizing, nor is it immediately obvious what the best path is to finding the law and its meaning. You need help, guidance and tutoring, That was the law librarian.