Quora Answer : Why did the city of Munich abandon open source and go back to use Microsoft software?
I don't know what happened in Munich.
But I do know someone involved in open-source in local government in the UK back in the day, when an open-source system was replaced by Microsoft.
At that point :
a) Microsoft dramatically slashed the price of the software they were selling. So as to make it more or less comparable with the open-source software (once support was included).
b) People were more familiar with Microsoft Office products and M$ convinced the local government that sticking with them would require less retraining.
c) Microsoft promised that Sharepoint integrated better and more closely with Office than the open-source servers did.
That was over 10 years ago. But I'd imagine that the sales-pitch is similar today. Cutting prices below official retail. Plus the lock-in of existing knowledge and systems. Maybe today there's also powerful, integrated cloud / SaaS offering in Azure.