If airlines would take greater responsibility for items in the hold, the size of carry-ons would decrease, I think. If a fee was introduced for your carry ons but not luggage in the hold, that too would reduce the amount of clutter in the lockers.
When you appeal to a persons wallet size, the results will come pretty fast. Quicker than using penalties or fines, because (as a real world comparison) we all drive too fast and rely on luck to not get caught.