Well, as the other person said, it was not a failing of LiMux. It was political. Munich had been ruled by one coalition throughout the lifetime of LiMux and after it went to a different coalition, they announced the switch back.
The manager of Munich’s IT department also publicly stated that they were surprised by the decision, because there are no larger technical problems and compatibility is resolved by providing virtualized MS Office, where necessary.
Coincidentally, Microsoft also moved its German headquarters from just outside of Munich’s tax region into Munich around the same time.