Comment by Ekaros

Depending on goal of library and possible value of book this seems reasonable enough process. If you have library with goal of sharing popular enough content, keeping the popular books and removing truly unpopular that do not have significant value seems reasonable.

Unlike digital world where storage is cheap, in physical world it is limited. Thus focus on what the customers want is reasonable.

Archival libraries are different game. There keeping at least one copy is often reasonable.