You have to preheat a pizza stone for a very long time (EG. an hour), to get it all up to temperature right through to the center. It has to be able to transfer a lot of heat very quickly, and it can't do that if only the outer few millimeters are hot.

Sometimes I want a really thick high-rise crust, so I'll cook the pizza skin without topping until it is firm and slightly brown. Then I add all the sauce, toppings, cheese, etc. and put it back in the oven until that all browns and sizzles. Comes out rather like french bread pizza.