Most libraries track circulation of their catalog. If nobody is using the classics, they're going to get weeded. Most libraries have limited shelf space, and it's best used for things that people are using.

Archival can be part of a library too, but I think a reasonable tradeoff is interlibrary loans, public catalogs, and considering copies in other libraries while weeding. Some library systems can also move items to non-public stacks which may be less space constrained, and only access them on request.