You are extrapolating a lot from your own experience. I can confirm from my own upbringing that my family always had junk food or soda in the house - eating it was a daily occurance, and it was re-added to the grocery list each time we ran out with little thought given to the potential health impacts. And we only took home leftovers if it was, like, a really big meal.

Sure, not all Americans are like this. I'm not like this, and none of my friends are. But I am aware that I very much live in a bubble.