Just as an example go back a few more years for resale value. First gen Dodges with Cummins are going for more than many second gen trucks. A nice flatbed one just went on ebay for $15k. Resale might dip on the diesel trucks a bit, but they come back up, unlike a gasser.
Gassers may get the mileage, but they don't maintain that mileage under load as well as a diesel. Also, talking money at the pump, some people obviously pay more upfront for a vehicle to spend less to operate. Take into consideration interest rates on auto loans compared to credit cards.