Those kei trucks are great for urban areas though, where the density is pretty high. If you do deliveries in a downtown area, having a smaller truck is great for zipping around packed streets and fitting into small parking spaces.
That's why people love them. Also, they're very efficient on gas.
If you need the ability to carry a lot of stuff, but a pickup like the F-150 is too big to go around downtown, a Kei is really good because they can haul a lot more than a car, without taking much more footprint.
Of course, the main reason they're illegal is not safety, it's because they're small, lightweight, great on gas, and that is not the general messaging the Big 3 want to make. Because big trucks and SUVs are way more profitable per vehicle than a smaller truck.
The reason they're illegal is heavy lobbying by the car companies to make them illegal because they don't want to compete with people finding smaller trucks much more useful for going around town, especially for work trucks and such. Pickup trucks are used for work, and if you're forced to buy a $70,000 F-150 that gets 8mpg even if it's way more truck than you need, that's better for Ford than if you discover you can get a Kei car for $15,000 all in, that gets 30mpg and you can actually park it and go about your day.
The Big 3 have been giving a narrative that only big vehicles will do since the late 80s, which is why there's the rise of the SUV as the family hauler over say, the station wagon. Or why SUVs over minivans.
Part of the auto tariffs is because the Big 3 refuse to make smaller more efficient vehicles and that's a niche that Japanese and other foreign makes did to invade the US in the 70s.