The Pentagon has a ton of restaurants inside. There's literally an official mall-style map of all of them right here, I count almost 30: https://www.whs.mil/Services-and-Information/DoDCC/

The pizza index is specifically about late-night pizza orders, when presumably most of those restaurants are closed (though some do appear to be open 24/7).

If the pizza-indicator is still observable, then there is insufficient internal capacity (or perhaps it would be more correct to say insufficient at the right times) to mask the signal