My local library wasn't meant for academics, but the problem is exactly the same. In fact, I'd expect a library with those kinds of books to be more amenable to trimming the collection: you often don't have a romance novel in mind, you browse for one that piques your interest. I'd be surprised if anyone was actively browsing shelves for philosophy books that seemed fun. That's the sort of stuff you go to the card catalog for.

> I do not understand why you would buy 20 copies of one book when you could have it and 19 other books.

Easy answer. Libraries know what their clients will check out. Often, because books are requested. If fifty people wait-listed the last big Dan Brown book, the library buys enough so that those people aren't waiting months to get their turn.

And yes, it's frustrating for librarians. Nobody likes buying lots of books that are not especially good. But that's literally the whole point of the library. Providing access to books that people actually want to read.