cheeseburgers are tasty

Why are we so addicted to cheeseburgers and junk food in general? It is certainly not because of our human nature because cave people did not have any kind of processed food to eat. The thing we today call comfort food is defined at the things we love to eat when we know we should not eat them. We love the fat and all that is bad in food and since birth we learn to hate carrots and other vegetables.