You didn’t answer the question.
What is wrong with using Fort Irwin?
Do you understand the importance of using realism in maneuvers? If there is a Beslan or Mumbai type attack, they’ll have to transit across civilian areas. What help is it to practice in a small enclosed space? Nobody is going to attack them at Ft. Irwin.
My only point is that there is nothing at all new here, in fact these are very small indeed compared to some past war games.