It’s that, plus other factors. The regulations are more lenient, it’s easier to get a more efficient engine in with more mass to work with, it’s easier to pass safety ranking checks, and it’s easier to put comfort features in that consumers want.
Putting a large crumple zone on a compact isn’t as easy as putting one on a giant truck.
(Note this isn’t saying big cars are more or proportionally more efficient , but that the efficiency advances they’ve made over the years are easier to implement in a large engine)
It’s that, plus other factors. The regulations are more lenient, it’s easier to get a more efficient engine in with more mass to work with, it’s easier to pass safety ranking checks, and it’s easier to put comfort features in that consumers want.
Putting a large crumple zone on a compact isn’t as easy as putting one on a giant truck.
(Note this isn’t saying big cars are more or proportionally more efficient , but that the efficiency advances they’ve made over the years are easier to implement in a large engine)