U.S. diesel emissions requirements are much more stringent.
Having lived and worked in Australia where there aren't U.S. laws, it is a myth that this somehow means the roads are full of these wonderful vehicles. Moving goods and acquiring vehicles just plain cost more there, and smaller (and more expensive) trucks mean more trips. The third world is not exactly some panacea either.
I think preserving good paying union jobs in the automotive industry is important. We have already lost so much industry, and it won't work to lose even more.1. The "Chicken Tax" first imposed by the Johnson Administration that imposes a 25% import duty on light trucks but not cars: https://en.wikipedia.org/wiki/Chicken_tax
We'll keep our American made trucks. You're welcome to move somewhere else if you think trucks and cars are so much better there.