Many US states have laws preventing people from registering these kei class trucks.
For example, https://dmv.ny.gov/registration/how-register-imported-vehicle
On that page
KEI-Class vehicles cannot be registered or titled in New York State. (Authority: Section 400-a of NYS VTL)
I think any person who has a hand in making those laws would say it's for safety. Though I also think many people looking at it and comparing it to other vehicles that are allowed would call it politics/corruption/stupidity. I personally think it's politics