I have seen the pizza go the full cycle.. from a small Pizzeria making good pies, getting popular, getting bigger to the point where they realize that most people won't pay for good food.
Well they will pay for fashionable food, or to be seen in the right places, but when you're competing with pizza pizza.. you better be using the worst ingredients to provide the rock bottom price.
Now a lot of this is from the perspective of an old guy. I haven't been keeping up, and there are some new places that are still really good. This is a very recent phenomenon.