It's not that the food tastes good. For some, its the convenience factor - why spend 2 hours on meal prep, eating, and cleaning up when complete satiation is 5 minutes away? For others, it's the context under which it was eaten.
Contextually, fast food was a "reward" given by lazy parents during childhood, and the food was just a byproduct of the experience. Later on in life, when things suck and the person finds themselves unable to cope, they use the food as nostalgic means to try to relive the pleasant childhood experience of going to a fast food restaurant. However, like any person with an addictive personality, they find that the high is short-lived, and they eat more and more to try to keep up.