Well, the problem is also that people seem to try to carry a massive amount of carry on to avoid having to pay for checked.
Nearly every time I fly I'm amazed at just how many bags people try to count as carry on. Plus if the crew pull them up on it, they make such a big deal when you think they'd have to realise they've got way too much (seen it a few times where someone has a roller bag, backpack and other bag)