There are people who think US corporations should be able to compete without any hindrance.
Having a car with lower emissions might mean it is more expensive, or less efficient, or have some other factor that makes it less competitive.
They think competing is better for the environment than regulation.
There are theories that support this, "the solution to pollution is economic growth"
https://en.wikipedia.org/wiki/Kuznets_curve#Environmental_Ku...
though not without controversy.