The same reason anyone buys anything that they don’t use, they think they’ll enjoy it but in reality they don’t find time or lose interest.
But those things aren’t the answer to OP’s question, are they? I’m sure that out of all the Harry Potter or DaVinci’s Code or whatever whatever popular book you look at there’ll be a nice % of books that haven’t been read, but I’m pretty sure that a majority of.peoole that buy them also end up reading them.
The more reasonable answer would probably be something that’s popular but not necessarily something you read. Like others have said, a dictionary, cookbook, or book related to some other skill. Those are a lot more likely to go unread
The meaning of OP’s question seems blindingly obvious to me, as long as you don’t take it too literally…
I’d say the DaVinci code would be a good answer, I’ve got a copy that I’ve never read. Same with the Harry Potter books as well.
The girl on the train is another book that everyone seems to own, but nobody reads.
