No, this is not the real reason, the real reason is Diesel gets twice of MPG than gas, plus twice of torque as well. 2014 diesel truck has at least 800 ft lbs torque, while average cars have only 150 ft lbs torque. Older steam power train produces 900 Ft lbs torque, meaning that 2014 Diesel truck has almost pulling power that steam engine has.
If you look carefully, I have seen F-250 and F350 powerstroke hauling 5 cars on the trailer.
