Kei trucks due have the issue of not being great to actual haul things in the mountainous areas (a tradeoff of the small engine). They make a non-kei version that has a bigger engine for situations like that.

That being said, I think if roads and such were bigger here (Japan), we'd definitely seem more American-style vehicles. Miyazaki (Ghibli) had lots of environmental themes in his works and it wasn't because people were doing a great job of taking care of the environment. I have seen American trucks driving around Tokyo (which is silly because they can't even fit down some streets) as well as sports cars and even hummers. Yeah, some are driven by foreigners, but there are still plenty of Japanese who import and drive US vehicles. The second biggest thing stopping that is the cost of getting it over here, inspected, registered, etc. Some humans just want those and want to show off their status and Japanese people are just people, after all (as much as the internet loves to pretend otherwise).