Whatever the ideal is, the reality is that everything old is pulped to make room for the latest political fare and romance novels, especially if it’s not been checked out lately. An ideological criterion is applied on top of this.

God only knows how many works have been consigned to permanent oblivion because they were only of local or niche interest, when even notorious classical works that were read for a thousand years are no longer available in many library systems without ILL. (And sometimes not even then.)

Modern libraries are for entertainment, not education, with few exceptions.

Aside: do not donate books to the library unless you do not care what happens to them. If the library cannot sell them they will be pulped. They are almost never added to collections.

Aside2: for some reason rescuing library books from dumpsters is considered theft by some librarians, so be careful.