I'm not saying aerodynamics isn't important, but only that significant changes need to be made that smooth the transition between road and rail so that single truck/trailer combinations aren't being used for stupid trips across the continent that could easily be accomodated by rail and are only used for local deliveries.
However, making rail responsive enough to tie into the just-in-time manufacturing sector is more difficult than it should be.
Plenty are in the US. A lot of people from other countries don't appreciate just how much open space there is to cover here.
The ones you see driving around at 70+mph are usually owner-operators who don't have their trucks governed.
Anecdotally, as someone with a lot personal experience driving an RV down the road capped at 65mph, I get passed all the time by big trucks. I do see plenty that are likely governed at 65 though.
Isn't this only true up until around 50-55 mph? IIRC, at the speeds truckers see in the US, especially on rural highways, aero dominates.