The FOSS movement in Germany always seemed to me a tiny bit more mainstream than the one in the US. Tech publications report more on Linux happenings (as opposed to the sometimes intense Apple focus of US tech publications).

Linux also has more market share in Germany than any other western country, I think.

According to statcounter, Germany has the highest usage of Firefox and fourth highest usage of Linux (behind Ireland, Greece and Luxembourg) among European and North American countries. Additionally, you have the Chaos Computer Club, which is somewhat prominent and could influence the thinking about FOSS.

Why would the US government try to avoid Microsoft? It's a well-known local company. And the government can get a good chunk of the license costs back throughout company and employment taxes.

In the eyes of the FSF and people with similar ideals, the benefits gained by spending that money on free software dwarfs the tax revenue gained. The German people seem to have enough support for free software to at least make the government notice, which does not seem true in the US.