I think attributing it to any one cause is kind of silly. It's a fact that American cities are much more car centric with higher speeds and fewer areas with traffic calming measures, all of which make the roads much safer.

Daily highway driving is much more common for commutes and errands, suburbs have dangerous arterial street designs.

I'm sure there's more to it, such as licensing and vehicle safety measures, but American highway design (and making local roads into mini highways) is a part of it.

Also the EU measure is EU-wide, and not all countries in the EU are as strict as say Germany for licensing.