It's not just a money thing, though. Even on airlines where you don't pay for checked bags (except excess) pax bring on ludicrous oversized bags that are bigger than the allowance and more numerous. That's surely because they don't want to wait for an hour at the other end for their baggage.
I don't bring on oversized bags but I certainly try to travel light and not check anything in if I can help it for that very reason.