It's because in addition to fuel being cheaper in the US, many EU countries tax you on engine displacement, CO2 emissions, fuel economy etc.

Well yes, but watching American car reviews(as European) leaves me puzzled - reviewers often describing 3.0L V6, 200bhp engine as small and low power, and discussing if it's not dangerous to merge on the highway with it, while over here you get a 1.0L 110bhp engine in a large family SUV and it isn't even brought up as an issue. In my last car the base option was 90bhp, and the "high performance" model was 160bhp. I guess in US that would be described as a horse cart. That's despite the fact that even the 90bhp model had no issue keeping up with 80mph traffic.