Public Libraries in the UK must be rich

As part of the marketing campaign for the book Teen Valour my publishers have sent a free review copy of the book to local authorities to see if the library department would want to receive gratis donated copies for their branch libraries. No commitment and no expectation of purchase. In each case before sending the book  the publishers phoned ahead to check the correct person who should receive the book. If the local authority said no to the offer nothing was sent so it can hardly be called junk mail.
The publishers have sent out 30 such review copies to different local authorities and have so far received only one response/acknowledgement in the 6 week period since the books were sent out. That respondee was pleased to receive copies.  The rest of the libraries didn't bother to respond. The publishers made some follow up enquiries and got the response from the libraries that they prefer to go Library Suppliers and they do not accept unsolicited books.
In effect the libraries outsource their selection process to third parties (effective monopolies) who then in turn make a profit on that outsourced activity. The libraries think that it is cheaper to buy the books than accept donated new copies.
I ask just how much does it cost to stamp a book with a library stamp and record the entry in their catalogue? Are libraries actually still interested in books?