There are a number of reasons that the trucks are different, mainly having to do with length limits, emissions regulations, protectionist safety laws and axle weight regulations (though these have an affect more between states in the US and countries in Europe). read more
Cabover trucks took full advantage of the trucking industry length laws, in effect at the time. Class 8 highway trucks in a COE style, are no longer manufactured in North America. Since the length laws have changed so much to allow longer units on the roads, there are no longer the same advantages this style. read more
Parking spaces roads and size are at a premium in Europe, It is more convenient there to have the most cargo space for the smallest footprint, thus the cab over trucks. Uhaul trucks are still cab over. In the US we are not so much in need of the smallest footprint for a truck and a straight box truck would in my estimation be cheaper to build. read more