I've worked in university and public libraries. Donations are generally not helpful, unless it's a small local library that really struggles to get stock. Uni librarians and academics will select books dependent on what courses are running, what is requested, and order from specialist suppliers who do all the processing, so they're pretty much shelf-ready when they arrive.
Doing that in-house costs time and money, so donations aren't really free or straightforward, so everywhere I've worked donations sat in a box or on someone's desk for ages, sometimes months, until a member of staff had a spare hour to go through them. Most were then given away, because we either didn't need them, didn't have the resources to process them or enough shelf space. It's nothing to do with librarians' own views on a book, just that all libraries have acquisitions policies.
If you want to get them to Sussex students, then either get students filling in request forms for the book (if they don't have enough copies already), or send a load to Brighton charity shops. Or give them to your local charity shops, book hubs, etc.