Good radiator space was definitely some of it, part of the requirement for the engines and transmissions to last the like million+ miles truckers want out of them is to have more than merely sufficient cooling in order to keep both the engine and transmission to stay the same temperature no matter how hot it is outside or how hard they need to run the engines to get up a hill. Of course that is along side other semi-truck specific equipment like bypass oil filters that have a MUCH finer filter to remove smaller metal particles that would otherwise just pass right through the main oil filter. More variable operating temperatures and worse oil filtration might be fine for consumer vehicles that are mostly rusted out trash out by time they hit 300,000 miles, but you wouldn't want to have to buy a brand new semi-truck engine every 3 years.