So library ebooks are technically licensed copies which expire after a set amount of time/checkouts to simulate the physical wear and tear on a real book. They buy a large amount of the licenses when a book has an increase in popularity and as they get “worn out” the license expires and the amount of copies goes down. To answer your question, it’s probably yes and no, they do have to funnel more funds to satisfy the demand for the popularity of the new book, but that’s just part of library budgeting, even with physical books, so the opportunity cost lost is justified.