It's not about the testing, it's about the SUV/light truck loophole that's allowed automakers to build larger vehicles that aren't counted for CAFE calculations. Here's one article about it: https://www.distilled.earth/p/the-loophole-that-made-cars-in-america
https://m.youtube.com/watch?v=jiH97O542jA?t=10s
General Motors
It's not about the testing, it's about the SUV/light truck loophole that's allowed automakers to build larger vehicles that aren't counted for CAFE calculations. Here's one article about it: https://www.distilled.earth/p/the-loophole-that-made-cars-in-america