@robinsyl The question is the wrong one anyway. The correct question is "why *would* people return the books on time if there are late fees?"
(And indeed every time a library has actually trialed abolishing them, and looked at the data, they found that the late fees made no noticeable difference. Which doesn't surprise anyone who knows the first thing about welfare systems)
@joepie91 I had an interesting convo with a friend about this before. My local library has no late fees, and they asked me why would anyone return the books on time if there are no late fees. Because the library is a public good and people respect it?