mpg is directly correlated to size and weight. I don't know the details but apparently some concession was made to big auto on mpg that meant there was a looph

mpg is directly correlated to size and weight. I don't know the details but apparently some concession was made to big auto on mpg that meant there was a loophole and bigger heavier trucks didn't count against your mpg targets as much. That, not a focus on mpg, is the cause.