I was in the US for 4 weeks as a tourist, the amount of additional time and effort it takes in the US to eat healthy is mind boggling.
Where did you visit? I don't think I've ever lived in a city where it wasn't trivially easy to find healthy food in abundance.
All the ingredients you get in Europe you can get in the US easily
Are you sure the difference didn't mostly come down to being a tourist in temporary accommodation vs having access to a familiar grocery store and your home kitchen?