I think it's a case of car manufacturers not optimizing for safety where there's no federal regulations for. There's no incentive for manufacturers to make their cars safer for scenarios not tested by regulation.

I watched a video on car safety about this [1] - initially regulators only tested for head-on collisions, but when they started testing for slightly skewed head collisions (which is also a common crash scenario), all the cars that passed with flying colors previously failed in this new test.

[1] https://youtu.be/OnWpZKhDgAo