If it was gonna be cleared to drive on higher speed roads, then it would have to meet other regulatory requirements that would make it way more expensive than being the cheap workhorse that it is.

As a low speed vehicle it just needs basic safety equipment and technology. It doesnt have to meet a high standard of crashworthiness. So on and so forth

By the time you get done making it a highway-safe truck according to those standards, you have something probably not far off from the $40,000 normal truck market. All those would be preferable to a buyer over a KEI truck if the KEI truck only cost like $5k less