If I had to guess, I'd say there being more metal involved is a significant factor in the number of deaths.
Two other possible reasons: 1. Manufacturers popular in Scandinavia, like Volvo and now Tesla, make much safer cars than their competition, and 2. It is ridiculously easy to get a driver's license in America compared to Europe. If you measured "graduates'" driving ability out of the gate, I'm sure Europe would come out on top. (Though, American roads being much larger and safer in general might compensate for this. I'm not sure what the article is talking about when it implies Swedish roads are safer -- they're a mess compared to America's in that respect.)