Need to add:
Crash certified bumpers to 5mph Engineered crumple zones Re-enforced A and B pillars Re-enforced doors Air bags
And I'm quite sure I've forgotten more than one other thing they would need to add Kei style trucks to make them roadworthy in many states. And once you make those upgrades, plus the cost of all the federal testing that would be needed, how much do you think one of those little trucks would cost?