A core problem is a customer thinking that serving size and price should be proportional. Most of the real costs are independent of portion size, i.e. real estate, capital, and labor. The raw ingredients in restaurant food just aren't that much of the total cost. The rest of the differences between fast food or fine dining come down to the quest to find local maxima in this problem space.

Fast food can bring the total cost closer to the raw ingredients by increasing the utilization of real estate, capital, and labor. A fine dining restaurant needs to dedicate much more real estate and staff to each customer, since they cannot serve as many customers in one time period. At the same time, they probably need at least some higher cost ingredients to satisfy the different expectations of a customer willing to pay higher prices.