You do see new minitrucks in certain non-road settings in the US, but yeah, they aren't street legal. Some folks import them for use as UTVs: https://usminitrucksales.com

It's the same somewhat bizarre logic that makes it fine to register say, a 1969 VW Beetle in the US, but not a 2004 Mexican Beetle that's no less clean or safe. The older stuff gets grandfathered in because at that age there's hardly anyone willing to bother. But if new minitrucks were road legal, they'd be everywhere, and there might be an epidemic of minitruck highway deaths, etc.