If there was demand the trucks would be sold here. Much less need for cab-overs make it a different market.
Not entirely true. The 25% "chicken tax" on truck imports makes it economically prohibitive to market cargo trucks made outside NAFTA in NA. Various mfgs have gotten around it by selling trucks as "implement carriers" (Unimog U500) or as "incomplete vehicles" (i.e. dutied at the 2.5% auto part rate) e.g. Japanese pickups (for a while) without the bed, which was mfg'd and installed in NA.
I'm not sure what the duty situation is for Mitsubishi Fuso? I'd guess Isuzus are at least partly assembled at GM plants in NA.
Charlie