They couldn’t deploy until someone gave the order to deploy.
This authority to activate the D.C. National Guard has been delegated, by the President, to the Secretary of Defense and further delegated to the Secretary of the Army. The D.C. National Guard is the only National Guard unit, out of all of the 54 states and territories, which reports only to the President.
Basically Trump and the above listed people didn’t order them to them to be deployed.