What even is that?
Well, it started as a form of yellow cheddar that was called "American Cheese" overseas and "Yellow Cheese" or "Stone Cheese" in the US, but after the invention of processed cheeses, the term was popularized to mean "Processed Yellow Cheese."
Technically, a processed cheese is just a pasteurized, homogeneous mixture of two or more cheeses; so while I agree that singles and similar "american cheeses" are pretty nasty, there are some good "American Cheeses" out there.
Most, however, are a by product of our extensive wealth.
Also, some overeating habits arose out of living through the great depression. My grandmother was raised in a way to always finish what was on your plate because her parents lived through a time where food scarcity was a real bitch.
That carried through to my mom who grew up fat when always finish what is in front of you was paired with rich meals due to living in the peak of middle class America wealth.
The nation is getting more health conscious because we are realizing the damage that way of eating does to our bodies and environment.