I always had an intuition for this. Coming from southern Europe where the default is you cook your food, I'd always had the impression that Americans were way too casual about eating out, like it's not even a point of consideration (consequence of much higher disposable income, and comparatively more expensive basic groceries). Now I learned a nice phrase for this, "food environment".
I moved to the usa from mexico around 10 years ago, I eat mostly the same as I did back then (mostly home made food) with around the same activity level and I still gained like 15 kilos
