I think it has something to do with cheap foods being the highest in fat and calories. People tend to think that all Americas are rich and can eat the healthy foods, when in fact only our top 8% have money. The rest of us survive on mac and cheese, fatter cuts of meat and the cheap fast foods. Most likely because it's what we can afford both money and time wise.
The driving issue is big here in the west. The closest big airport is a 3 hour drive away, then we get to get on the plane and fly to our destination. Most commutes to work are on average here where I am at are over 13 miles, a good deal are over 40 miles. I am lucky as my work is 2 miles away from my house, and the grocery store is 1.5 miles away and I am considered to live within a short distance of things. However, I am not the norm, I am the exception.
I also believe the serving sizes are way too big here too. But from what I have seen the rest of the world is catching up fairly quickly in the weight issue.
Maria once said that perhaps the hormones in meat and veggies is part of the problem too, which it could be.
Or maybe its because we are headed for lean times and food will be scare so we are all stock piling our calories.