Bigger and heavier vehicles (more specifically “trucks” which aren’t legally defined by their beds and encompass virtually anything larger than a simple sedan) are exempt from the majority of fuel economy standards. As a result many auto makers have just straight up stopped making “cars” and shifted entirely to larger vehicles because they can get away with more emissions. Yes, a 2023 SUV is slightly more efficient than a 2013 SUV, but so many more of them are being sold instead of cars that the overall emissions are way higher. I love my Ford Focus from 2017 but Ford literally cancelled every single sedan, coupe and hatchback other than the Mustang and now exclusively makes SUVs, trucks and a single sports car.

That's the whole point, what good would it be to compare equivalent vehicles, when people don't drive equivalent vehicles? They drive bigger and heavier vehicles on average, negating efficiency gains of newer vehicles.