Have you seen how people in the U.S. try and board airplanes?
The most organized boarding experiences I've had in the West have been in the UK, interestingly enough. It seems the British are innately aware of how to queue correctly and in an orderly fashion. Japan and Singapore were also incredibly orderly.
I've been to a lot of places around the world, and I'd say the US is on the upper side of the middle of the pack in boarding efficiency and order, and it's better than boarding the plane in some European countries even. Considering the US market alone accounts for a significant chunk of all air travel globally, efficient boarding isn't exactly something people ignored. There's actually a lot of research that's gone into it.
I'd say the US is capable of doing things organized with large groups of people, but only if there is a social standard set for that situation and environment. Right now we have no such standard for an evacuation situation.
The Southwest cattle car style works better than anything else I've seen. Sure, it sucks to be one of the last boarders and be sentenced to a middle seat in the back, but that's something that can be fixed if you're better organized and more punctual next time you fly.
When you see the people checking seemingly all their worldly possessions, it's mostly families.
I don't doubt there's some effect at the margins but people mostly just prefer to carry-on if they can.
I partly blame roll-a-boards. They take up more space and are less flexible than soft luggage.
I also think that in the "old" days, carry-on garment bags notwithstanding, business travelers were far more inclined to check because they needed a lot more clothing to be properly dressed. I used to check luggage when I traveled on business. I haven't done so, barring unusual circumstances (gear for personal travel or commercial materials), in well over a decade.
Plane boarding is kinda fascinating.