For what the average person uses their $50k pickup for, you most certainly can. Do you really imagine most pickup trucks in the US are hauling bricks on a dirt road up the side of mountains?
You think a Kei truck can't make it up a mountain with a load of bricks? It may not be the fastest, and the biggest load of bricks it can haul is gonna be smaller, but let's not pretend a Kei truck can't go to Home Depot and back again with a decent amount of stuff. Like smaller trucks in the US, like the Ford Ranger or Chevy S10, they do just fine if you don't abuse them. If you do, giant 2-ton trucks don't last either.
No, I imagine the average person in the U.S. is using their truck to drive to and from their office job and taking their kids to and from school. And for that these tiny trucks obviously would not work.
You said it yourself. People aren’t buying trucks for their function. They aren’t hauling bricks up mountain roads. So if it’s not about function, then it’s about something else and a Kei truck might not fill that role.
It’s like people who spend thousands of dollars on a wristwatch. They don’t do that because they need to know what time it is.
