>>514097601 (OP)
1. Massive amounts of food
2. Post-WWII prosperity made everything cheap
3. Unsustainable industrial farming practices rape the soil and animals, resulting in reduced nutrient density
4. Food companies use industrial processes to reduce cost while making unhealthy food more palatable
Put these together, and you have a massive, easily accessible supply of slop to gorge yourself on.
Bonus:
5. Sneed oil salesmen fabricated evidence that saturated fat (the competition) is unhealthy, and vegans on the standards boards kept the fraudulent science going in perpetuity. This means that food is never filling, since saturated fat triggers your body's fullness response. (To see this in action, have a 500-calorie carb breakfast one day and a 500-calorie dairy breakfast the next.)
6. Liberals have wholly discarded the idea of authority over oneself, so self-control is absent from many Americans' dietary habits
7. Liberals have also discarded accountability, so it's never your fault if you're fat
Final verdict: Worthless, empty-calorie food, in massive quantities, with no mental or physical indicators that it's time to stop eating