I thought it was due to fuel standard requirements and loopholes between autos and light trucks like the F-150.

Cars and mid size SUVs all seem to be converging on the same shape with minor differences where as trucks still have some individuality.

So I went to check this supposition out and whew, I’m confused.

CAFE standards, harmonic means, compliance flexibility, offset credits are all more than I can wrap my head around from my smartphone.

Not to mention trying to read the actual CAFE regulation is very convoluted.

Anyways, I thought I had an answer for you but all I’ve got is a rabbit hole in crawling out of.

https://reason.org/e-brief/cafe-standards-in-plain-english/