The linked headline from the OPs post about the switch:
> Linux in Munich: 'No compelling technical reason to return to Windows,' says city's IT chief
https://www.techrepublic.com/article/linux-in-munich-no-comp...
The reason was probably a shift in IT management who wanted to keep things "simple" with some vague thing about keeping one platform since they had kept previous windows machines around which were apparently "absolutely needed". It takes heart in the management to keep Linux around, which isn't always a reliable thing. Even when there was no "technical" need to use the more expensive Windows option.
But this sounds 100% like a Microsoft sales/marketing job, which they are amazing at. They've really perfected selling to big firms, which you could see with the growth of Azure. Which I witnessed when they unleashed their sales machine on startups to get them to use it, and it was quite interesting to see in action.