> Which is almost certainly a combination of the complexities of govt IT procurement, the needs of non-technical users who may only be familiar with Windows & MS Office, and the enterprise management features of Windows that aren't as good in most other OSes.

... and if I were to guess, there's definitely backroom deals between the US government and Microsoft. There's no way all the phone home stuff is even included in "Windows for SCIF".

if you mean as in Windows phoning home in normal installations, a Windows Enterprise install stripped of most unneeded components with Group policy won't really "phone home"

and you can always just airgap the thing