Just to say it the Lower Saxony example is not quite correct. The situation is that they started using Solaris a Unix system in the 90s in the tax department. When Solaris was no longer really developed, they opted to switch to Linux, as it was easier to migrate. However to unify German states tax departments, the previous state government opted to move to Windows. However the migration has so far failed. Mainyl due to the systems never having been designed for Windows in the first place. The other large user of Linux in Lower Saxony is the police and although they migrated from Windows to save some money, they too had problems migrating back as it was just too difficult.

That is just the reality of it. Software is sticky and once you migrate it often stays. Even when politicans do not like that.