[jabl]

Footprint is at least partially due to regulations. EU regulations are much stricter with dimensions, whereas in the US the limit is more the weight.

Technical development might have some impact as well. I remember as a kid many trucks needing bigger engines (e.g. sand or concrete transport) had the cab-behind-engine layout, but nowadays those are more or less completely gone. Maybe turbochargers and intercoolers allowed a sufficiently powerful engine in the cab-above-engine layout?

[Gwypaas]

American trucks are actually lighter than European. 36 tons compared to 40 or 44 tons for most of Europe.

The entire Nordics allow 25m (83 ft) trucks up to 60 tons.