I think there are at least three prime reasons why 'fast' and 'quick' service food concepts will always be the big dog among all franchising segments.
First, having grown up in the restaurant business, I can echo back what my father believed when he opened his first successful location, which was a 'quick service, Italian menu' that served the lunch crowds in a manufacturing area. His thinking was: one, people were always going to eat, therefore the market would always exist; two, because the market already existed and the present competitors were busy, he felt he could beat them by providing a better product with better service. Whether his thinking was right or wrong, it worked for him for nearly thirty years, so he was obviously on to something.
Second, and frankly this is probably a better bet for explaining why food lends itself well to franchising, to do well in the restaurant business, there must exist a sound system that is followed repeatedly. Therefore, those who have figured out a successful repeatable cycle can sell and teach that visible system. Any fee for service franchise consultant worth their salt will always be looking for signs of a quality system. Had franchising been in vogue in my father's time, that could have been his next logical step because the restaurant ran like a Navy fighting ship. There was a system for everything.
And third, brand awareness (both for the positive and the negative) is fairly rapidly built around food. People either like what they ate or they are gone.