Diet is part of the problem but a big part of the issue is the inherent sedentary lifestyle associated with American infrastructure and suburban development. If you design tons of housing in a way that encourages people to utilize cars as much as possible, invest as little as possible into infrastructure like public sidewalks and bike lanes, etc then don’t be shocked when your populace becomes fat and lazy, especially when you combine this with a carbohydrate/sugar rich diet. The EU has a worsening diet. Japan eats more carbs than America. What’s the difference? They naturally walk much more as part of their daily routine because their governments invest in communities rather than stealing tax money to launder to military contractors.

Whenever I travel outside the USA I am always astounded at how little effort I need to put into getting my daily steps vs when I am at home. At home it is a concentrated effort