The loophole for the kei trucks is that they're more than 25 years old, so they get "antique car" status in most places (except where they're now stamping that out of course). But lots of other antique cars are allowed on the road, and while kei trucks are inherently unsafe (they don't conform to federal safety laws and don't have any real crumple zones because of their size), the other antique cars are also just as unsafe, if not more so. But you don't see any of these places trying to ban people from driving their antique Model T or '55 Chevy.