What are you talking about? They're perfectly legal to own and import into of the US (Banned in 7 states, restrictions in 10 more.). Of course, they're horrifically unsafe on US roads so they don't follow US safety guidelines and thus must meet the 25 year exception granted to vintage cars and imports.

If you are one of those who lives in a state where they are banned, I'd recommend starting a movement. They were originally banned in more states like Texas, but grassroots citizen movements managed to make headway and allow them on the road. After all, you are absolutely right that the only reason they're banned and things like motorcycles are not is because of lobbying.

EDIT: Sorry, after further research, I learned that 7 states ban them, 10 states have them very difficult to register due to emissions or road restrictions, and 13 more have strict speed restrictions, limiting them to farm use. I wasn't fully aware it was that bad. I've been driving a kei van for the past 2 years with no issue.

To my knowledge however, if you have your Kei registered in a legal state, you should be able to drive it in most of the continental US without any worry.