There's more. Traffic accidents, Americans have more than twice as many fatal accidents as Europeans and 3-4 times as many as France/Finland/…, and the age of people dying in traffic pulls down the overall average. And of course crime. Americans shoot each other, and that's not just 95-year-olds, so that'll pull down the average as well.
What shocked me about the US when I went, was how much peptobismol people chugged down.
There was not one meal in my 1 week stay there that I could digest without issue.
Annual sales of Pepto Bismol look to be well under $0.50 per person, so while the American diet and food quality is appallingly worse than Europe, I suspect your one week of stomach upset is not be a great source from which to extrapolate.
Fair enough, maybe it was just the amount and variety of peptobismol products that I noticed were for sale everywhere. For example just in the Hotel where I was staying, they had a bunch chewable peptobismol gummy bears + the ordinary bottles for sale.
Eating food and drinking water in a strange place can upset your stomach even if the people who live there all the time are fine. This is a very well-known phenomenon.
This is why I cook at home a vast majority of the time. It also depends where in the country you are. You could easily eat healthy in LA, NYC, SF, Chicago, etc. but if you’re outside the major cities you can find it a lot harder.