Edgar Rice Burroughs probably isn't popular enough at your library to justify the resources and staff time for processing 42 books (especially without a dedicated cataloging department, which some libraries don't have these days), or the shelf space (and making room on the shelf for 42 more books in one spot is also quite the undertaking!). In a lot of countries you can get books pre-processed and added to the catalogue according to your library's requirements

If anyone else would like to avoid this, firstly don't donate books you don't want to part with in the first place, and secondly always try to talk to a selector or at least have a look at the donation policy or collection development/management policy.