And you can expense a >6000lb vehicle

I believe it's a mix of both.

https://en.wikipedia.org/wiki/SUV#United_States

The idea to introduce light trucks in passenger-car shape to get around pollution limits was the car manufacturers' idea. However, the US public ran with it and bought because of the perceived higher safety and social status that comes with driving a larger, heavier vehicle than everyone else. And they continue to buy to attempt to one-up each other even though the pollution limits now apply to SUVs as well as smaller passenger cars.

My understanding was that the American domestic auto manufacturers were getting their asses beat by foreign competitors who made much better cars. American companies could differentiate themselves with giant vehicles that wouldn't be practical in Europe or Asia. But because the giant vehicles became status symbols the low end started imitating them and now nobody sells cars in the US any more.

It's definitely a blend. I bought something HN would melt down over mostly due to the ride quality. I can drive from Houston to El Paso and not feel it.

I don't buy cars based on their pollution capabilities like some Captain Planet villain. Maybe other consumers are different.