Well, those are flat-out illegal here and importing them is made illegal except under a narrow set of circumstances so that the auto industry doesn’t have to compete.
No, it has nothing to do with competition, and everything to do with kei cars being underpowered. They can't keep up with the speed of traffic on the highway and they'd be a safety hazard to other motorists.
There’s lots of vehicles that can’t get on a freeway. There’s a sign on every freeway onramp. That’s something we literally already handle so that’s not the problem.
If that were the case they would be classed as Neighborhood Vehicles and so on. You can buy a golf-cart or 4x4 and drive it on public roads after all. Just not a freeway.
It literally, directly, unequivocally is protectionism and insisting otherwise is ahistorical and factually incorrect. It’s a vestige of a 1964 protectionist trade war with Japan that the US auto-industry lobbied their way into keeping even after the other provisions were lifted.