If they aren't, you can replace them with a cheaper, safer, more fuel efficient vehicle that meets US safety standards and is easier to maintain and register than a Kei, and probably at a comparable or far cheaper initial price than the Kei.
If they are using it for a practical purpose, you can't replace it with a Kei.
Either way, a Kei is probably the wrong choice for most US buyers.
(There are newer import-legal minitrucks that don't have the registration hassles, like Nissan Clipper, which makes the range of situations where the Kei makes a lot of sense outside of particular brand attachment even narrower.)
> There are newer import-legal minitrucks that don't have the registration hassles, like Nissan Clipper
I'm confused - the Nissan Clipper is a Kei car. Kei isn't a brand, it's just a description of a specific style of car (low weight, engine size etc incentivized by the Japanese government).
Often people living on large properties and in rural areas have vehicles that never hit public roads, and Kei car class vehicles or their equivalent get used every single day. Just think about the logistics of living down a long road on 30 acres - getting the mail, taking garbage bins out, moving tools, water, animal feed, debris, etc. Large trucks don’t even fit through some gates and Polaris/atv/small vehicle is often the best solution.