I think basically Linux didn't work that well for them more than "MS worming their way back in". It sounded pretty pragmatic in the case of Munich from what I read.
It looks like you've read only part of the story. The part I read was about Microsoft putting a lot of effort/money, including lobbying, into making Munich switch away from Linux, and now, as the sibling comments point out, Munich is switching back to Linux.
https://www.zdnet.com/article/linux-not-windows-why-munich-i... https://news.ycombinator.com/item?id=23190447