The implication I got was that the military personnel were likely under orders to not communicate with those inside "the dome." Otherwise, there's no reason why they wouldn't try some form of communication (like written) between the inside of the dome and the outside world.
But why? Military experiment on sheilding technology over small town went haywire?
We don't know. It's been two episodes. We just know that the red-haired chick was unable to draw their attention or get them to communicate with her the morning after the dome appeared. It's unlikely they didn't see or notice her (I assume military personnel are required to have peripheral vision) especially if she (as she suggested) took her top off. There may have been other references to communications to the outside of the dome no longer taking place.
What happens in the book aside, we don't know why the dome is there or what caused/is causing it or why communications to the outside have ceased. Again, it's been two episodes. I have a feeling they're trying to build a story and mythology here and not give everything away in the first bundle of episodes.