It probably also depends on the book. I have tons of outdated books on obscure topics within engineering, science, and computing. I doubt anyone would check out my 1995 book on the Vi text editor from a library. Although, if I’m lucky, perhaps it could be a collectors item some day. In reality, I’m probably going to just say “thank you for helping me so many years ago” and respectfully recycle the book.
I guess the libraries and schools can make the decision and throw out things they don’t find useful.