I did engage with your main point. Healthy prepared food did not exist in 1980 at a grocery store, the lowest income was more likely to need dual income and therefore not having more free time than now unlike richer people since 1980.

Here is the actual data that says people were spending 50% more on food despite more prep time and lower health food options:

https://www.ers.usda.gov/data-products/charts-of-note/110333

Your point is very socially satisfying but has no accuracy for why the majority of Americans are overweight or why the trend is global. (People buy expensive brand trash food but could in fact afford and find healthier food for less of their income now than in 1980.)