I figure what's happening is the governments around the world have started picking up people who are excited about open source and GitHub, as those people grow old enough to work in government. It wasn't long ago that GitHub was (in my eyes) mostly popular with early-twenties and younger, a demographic that doesn't usually work in government! But they grow older, some get hired in government, and they bring their enthusiasm with them.
And there are some exceptions! The CFPB, in particular, has a number of extremely talented young people doing awesome work and in-house development for them -- and they open source a great deal of work: https://github.com/cfpb