Problem is, too many options. Pizza.mobi is the only option. Once you add a second word to that, the skys the limit because your going to have to spend money to brand it no matter what that word is. Pizzanow, pizzafast, pizzaquick, pizzaparlor, pizzaria, etc, etc. A developer sees that they can buy pizzaplaces for $900 or they can register Pizzacall for $20. That just knocks the stuffing out of the value.
It's kind of like homes, as long as there is more land in the neighborhood to build homes on, it's hard for the home values to rise. If you've got that one home with the great view that can't be found anywhere else, value can rise quickly. You will need all the other real estate in the neighborhood to get bought up before this one has any real value.