Fast food has been designed and engineered to meet the tastes of the community it serves, no matter how big that community might be. McDonalds is an international corporation. The food it serves in America is different than what it serves in other countries. They spend millions of dollars in research to find out what people in this country like.
It is by no mere coincidence that fast food tastes the way it does.
Also Fast food tends to be fried and made with a lot of fat. Fat tends to hold all of a food's flavor.