[FooHentai]

I strongly suspect it's due to more than a single dimension. To name a few:

Emission controls, increased features (e.g. GPS, Seat warmers, lane assist), reduced fuel consumption, increased power, increased safety features, miniaturisation/lightening of components, reduced tolerances, materials specialization.

There are also more contentious but likely contributors, such as vendor lock-in (if you have to come to my dealer network form maintenance, I'm gonna make more money) or planned obsolescence (if you need a new car every X years, I'm gonna make more money).