Why do people associate "greediness" with people who eat Doritos and other junk foods?

Greediness is the consumation of the unnecessary. You do not need Doritos. You need basic foods in amounts relative to the amount of energy you use. More exercise, means more food. Less exercise, means less food. Doritos do very little in re-energising, they are purely a luxury, as is other junk food. Consuming it means you require more than you need to satisfy yourself. That is greediness, because there are those who can't even get constant supply of healthy food that they need. If you eat junk food, you are ingrateful for healthy foods, and that is greed.