People only 'abuse' carryon rules because airlines started charging to check baggage.
Originally, carryons were just that. For light traveling I used to avoid checking to save the delays of waiting for my luggage after the flight, but most of the time we'd check our luggage. Now, it's the other way around and people only check if they have to and do everything they can to avoid the fee. It's kind of hard to blame passengers too much for cramming as much as they can into their carryons, which makes loading and deplaning take longer and less pleasant.