[joe5150]

Public libraries have no such duty, no. Outside of the largest systems, most aren't fit to do this in a way that would materially achieve the goal of preserving anything, either in terms of space, equipment, or expertise.

So generally speaking, providing "what the public wants" is the entire purpose of public libraries. Obviously librarians exercise a lot of discretion about what specifically to buy and make available in the library, but most have long since moved on from paternalistic notions of needing to provide access only to The Great Books.