Hosting their own email is just a headache and adds overhead and takes resources away from the actual real stuff they are doing?!
92% of what the DoD does is normal business junk like ordering pencils.
I knew a guy who worked on a VR war the room for the DoD. Not like a VR battlefield simulator, but like... simulated folders being passes across simulated desks.
The point being that they're innovating away from the pencils. The future is digital pencils.