I can believe 800 programs.
Munich is a big place. I don't know what the specific responsibilities of its city government are, but I wouldn't be surprised if they include everything from policing to water quality to arts galleries to education to public transport, public health, parks, sports, dog registration, air quality, tourism, rubbish collection, libraries, cemeteries, city planning, housing, social services, animal welfare, food safety, roads and signposting, traffic management, taxis, land registration, civil defence, elections, and probably at least as many more things I haven't thought of. To say nothing of "reporting on all of the above to state and federal gov't".
Not having worked in any of those areas, I'm not remotely qualified to know what systems they may involve. But I would guess each of the above departments uses at least 2-3 separate databases that are developed specifically for Windows, and simply not supported on any other platform. Plus a dozen more applications I can barely even imagine.
This is what open-source zealots too often fail to account for. The world is complicated. Millions of developer-years have gone into building the systems that maintain everything around us. You can't redo all that just by waving your hands and saying "all you have to do is this" - somebody actually needs to put in several metric fucktonnes of work to make it so.
Now Munich has said, they're not going to be the ones to pay for that effort. And I don't blame them.