90% of the devices that are bought require windows. Every single microscope, ID reader, card reader, access system, detection system, defence devices, advanced cameras, radars, etc. provide drivers and/or software, that I know, offer drivers/apps only for windows.

Even they make a plan to move from windows, it will take years, in this time, every acquisition will be made for windows. A common use for these devices/pc's is more than 5 years. Heck i've seen tools that are used even after 15 years because they worked and no money/desire to replace them.

Of course you can negotiate, or request support for other operating systems, but that means extra money, training, etc. Even in the current state it's hard to get good IT people, programmers, sysadmins, etc. It will be harder to get linux admins. Also it will take years to teach people to use another OS.

And to end: have you seen custom software made for governments? 50% just slap a program that requires x version of .net, some c++ redistributable and requires to run only as admin or only xp, 40% just slap a java abomination or applet and call it a day, 9% make a nice piece of software but just like everyone else after they deliver the software they forget about the support or patch 1-2 things and they are gone. ALL OF THIS is happening mainly because the state doesn't have trained people and they don't know what to ask from devs & because they don't give a shi*t about they money they spend.