What is "outdated material" for a library? Isn't that precisely where you go to find "outdated material" is a library's archives?

Libraries have an entire concept of weeding, and numerous criteria for doing so: https://en.m.wikipedia.org/wiki/Weeding_(library)

Libraries are constantly bringing in new materials and very few are capable of constantly increasing in size to match. I believe national libraries like the Library of Congress tend not to weed, but they do have to offload material to satellite locations and storage facilities.

Stuff like the printed tax code of 1965 or Borland Pascal 1992 manual. Once you have it digitized it's a waste of space for libraries to have a physical copy because basically no one needs it.