[simfree]

Large SUVs with overcooked engines to meet emissions requirements (lower PM2.5 emissions at the cost of slightly worse fuel economy) get bad mileage.

Having all wheel drive or 4 wheel drive, high ground clearance, a poor aerodynamic design (driving 70mph or 80mph sounds bad in many of these cars) also hurts efficiency.

[Scoundreller]

Even when it comes to cars, often the US base model has a larger engine than the EU base model.

No idea why: speed limits are often higher in EU and often with more hills.

[avar]

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.

[gambiting]

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.