Two major reasons coinciding at the right time:

* They were alone. Munich is a big city ("biggest municipality in Germany" (there are bigger cities, but those are states as well)) but being an outlier complicated many things. For instance the software to order password from the federal printing agency was Windows only and required integration with hardware like fingerprint reader and stuff, being sole outlier makes this hard.

* Microsoft moved their German headquarters from a suburb to the city, thus pays local taxes.