There's been an upper class for whom food wasn't scarce for thousands of years. Socrates wrote about it, and it was looked down upon as type of gluttony and quite unhealthy. However, even those upper classes, who didn't have any food scarcity did not typically get fat.

Blaming it on food scarcity isn't the whole story. It's not enough that food scarcity stopped. It wasn't carbs either, as there are cultures without carb scarcity that weren't obese(Though we do put corn syrup in everything now).

My guess is that it's a dopamine addiction. We understand that sometimes we must do things we don't like, but the idea of eatings things we don't enjoy scares many people.

It's also how corps package food, and the ones that make their foods the most addicting(the most dopamine -> the most pleasure) survive.