The US actually has no pedestrian safety standards. Instead of implementing standards for pedestrian safety, the NHTSA chooses to educate pedestrians on how not to get run over:
Get resources on pedestrian safety tips whether you're walking or behind the wheel. Learn best practices on preventing pedestrian injuries and deaths.
www.nhtsa.gov
And big trucks aren't sold in any meaningful numbers anywhere else in the world that would have standards that influence their design.
The styling of trucks has a lot to do with marketing and image as well as massive capability. If you want to have rated payload capacity over 2k lbs in a half ton truck then you need to have suspension travel. If you want massive towing capacity, then you need lots of frontal area for bigger heat exchangers. So there's some amount of justification for larger, taller trucks but so much of it is just about making buyers feel more macho.