The average American doesn't understand the concept of "have your head on a swivel" and maintaining situational awareness of what is going on in two different directions. Or of just always be looking the direction that you're going (if you're about to stomp on the accelerator you better first be looking forward).
The massive SUVs and trucks just make the problem worse, but they didn't start the problem.
And that is apart from the horrible level of driver education, and education in general in the US, where a lot of drivers don't seem to understand that you actually need to stop for a right on red, or even that you need to yield to traffic from the left and just blow straight through the light.