Certainly there's the issue that eating at McDonald's is a more efficient way to feed a family when money is an issue. That absolutely contributes to our obesity.
But, at the same time, even those with money are eating far too much sugar. It's in everything. Buy a loaf of bread? Sugar. Soup base? Sugar. Cereal? Sugar.
Not to mention all the other processed chemicals that made Walter Bishop go nuts in the supermarket.
Worse, all these sugary things are pushed as "healthy." People think they're eating a healthy breakfast of cereal with fiber, not realizing the fiber is all crap fiber and the cereal is loaded with sugar. And chemicals.
It's extremely hard to walk into any supermarket, even Whole Foods, and not walk out loaded with unhealthy processed commercialism.