Why do so many take-out/order-out places emphasize on big food, and more of it?

Well it's also part of the our generation where money is more disposable and food is more available. We're also part of a very large population of obese people which can contribute to having bigger servings of food. In my experience, I'm not overweight, but sometimes I tend to buy the bigger item just to eat it all up and enjoy all of it without regard of the fat in it and thinking that I can just run it off..