America's standards for road worthy are just that much higher. IF you: start a car company, buy a bunch of them so the NHTSA can crash test them (thanks Mercedes-Benz for that one), fix them up so they meet modern Federal Motor Vehicle Safety Standards (FMVSS) (which includes backup cameras, among other things), fix them up to meet smog standards (for California), which means it'll also need a compliant OBDII port (and a Japanese OBDII port returning Japanese characters instead of ascii codes won't count), then yeah, it can be considered road-worthy and as a bonus, you can sell them.

It's just that all of the above is very expensive and a lot of work, if not impossible. Having to buy a bunch of cars just to get them crash tested is probably the most expensive part, but the rest of that isn't easy either. Coming back to the kei trucks discussed in the article, there's basically no way they're going to pass crash testing.

So it's not that it isn't a valid solution, just America has much higher standards for "road worthiness".

It's been "done" by MotoRex for R34 GTRs, though there is a bit of fuzziness as to their legality as they got shut down by the government. That's a whole other story though.

But if you're not going to use the vehicle on the road and just as a show car, or drag race car, it doesn't need to be considered road worthy and the import journey is much easier.