Because the fuel inlet for the Dodge/Ram Diesel trucks are sized for the highspeed truck stop fuel pumps. There was a time that some Ford and Chevy/GMC pick-up trucks were sized for the standard gas pump nozzle.
I know a friend of mine with a Chevy Diesel truck use too carry a funnel so, he could fill up at the truck stop fuel island when towing his 5er.
Jim & Jill
Sold: 2010 318SAB Cougar:New: 2016 Cedar Creek 34RL. 2008 Dodge 6.7LCummins the original 6.7L engine, w/68RFE Auto