This isn't necessarily regulatory capture or protectionism.
Half of all cars sold in the US are imported. Toyota, a Japanese company, is the most popular brand of car sold in the US.
So, yes, you can import cars all you want, they just need to follow US safety and emissions standards. These cars do not meet those requirements, so you can't import them.
If you didn't block them as imports, we'd have lots of people just go to Mexico and buy highly-polluting vehicles to save money, and our problem with smog in the border states would be much worse.
The interesting thing is Japanese companies generally manufacture cars they sell in America entirely in America, while “American” car companies manufacture their huge polluting machines in Mexico and maybe add one final part in the US so they can claim some work is done in the US. Japanese cars in the US aren’t imported while US cars are.
Nothing major is manufactured here.
The vehicles Japanese companies make for the American and US markets have no overlap. Nothing sold in America is made in Japan, and nothing sold in Japan is made in America. A lot of those vehicles are loaded up into tractor trailers and hauled off to their destination—Japanese tractor trailers that those manufacturers use aren’t large enough to haul American vehicles in Japan. Furthermore, the economics for manufacturing huge vehicles in a tiny country that can barely build for its own needs and shipping across the world wouldn’t make sense. The raw materials, energy, and real estate needed for the factories are simply far cheaper in the US.