Here are several plain facts about buses and trucks:
-Literally ALL modern city buses and motor coaches have flat fronts.
-A good majority of school buses in North America, however, have nose fronts (where there is a bulge in front of the driver in which the engine is contained). Flat-fronted school buses exist, but are far less common (back in 1989 when I was 10, I was quite surprised the first time I saw one; the next year, I got the chance to ride on one and I recall other kids gleefully remarking on how it was a different kind of bus; however, they didn’t seem to catch on).
-The cabs of tractor trailer trucks in North America used to be fairly common in two different styles: either with a long nose front or a cube-shaped cab with a flat front (two examples of the latter, both dating to the 1980s, are the vehicle mode of Autobot leader Optimus Prime in the original Transformers cartoon and the contraband-laden truck in the opening scene of “Beverly Hills Cop”). However, I don’t remember the last time I saw saw a flat-fronted tractor trailer truck in any North American context (oh wait - I do. A beautiful example, implied to be Optimus Prime, was showcased near the end of “Bumblebee”, the 2018 Transformers iteration, which was set in the 80s).
-In Europe, however, trucks with the cube-shaped cab are standard (the cab also generally seems a bit smaller than on North American trucks).
Are there practical differences for the prevailing styles of front that I have enumerated specifically being applied to each of the specific types of vehicle on which they prevail? Or is there an element of tradition/fashion/preference in any case? If flat fronts are good enough for all other kinds of bus, why not school buses and derivatives? Why are roughly cube-shaped truck cabs cool in Europe but ancient history in North America?