Having been to quite a few restaurants in the airport what struck me is that food is always so slow. In sit-down establishments you have to make sure you have at least an hour, because it takes so long. And even "fast food" like Mcdonald's isn't fast.
Is it because there is no competition? You cannot really go out and drive to another Mcdonalds. Is it because staffing is difficult, and thus they get lower quality employees (you have to go through the hassle of security every day, and airports are, surprisingly, not very easy to get to).