It's been going on for decades in all vehicle (cars, truck, motorcycles), That's the main reason for manufactures to have hybrids and low(er) emissions models in the fleet. Why would a manufacture waste their time making models so much lower than the current standards (like hybrids and EV's) if there's no benefit to that? Same as CAFE is done with emissions. Do a search. I did on-highway and off-highway emission compliance for a motorcycle manufacture for over 25 years and had to deal with it, so yes I know it still exists.

Definitions of Fleet Average Emission Fleet Average Emission means a vehicle manufacturer’s average vehicle emissions of all greenhouse gases, non-methane organic gases (NMOG), or NMOG plus oxides of nitrogen (NMOG + NOx), as applicable, from all new vehicles delivered for sale or lease in any model-year.(Break in Continuity of Sections) 12/11/2013 12/11/175.0 New Vehicle Emission Requirements5.1