Starting in 2014, trucks with a larger size were subject to less strict fuel efficiency requirements. This was because American automakers (who sell a lot more trucks) were unable to compete with foreign automakers that sold a lot of passenger cars that could bring their CAFE down.

However, the government screwed up the scaling factor and it basically became impossible to build a small truck, while larger trucks had much easier-to-meet requirements. That led to automakers basically abandoning the passenger car market, and upsizing trucks significantly.