I did a 4 year degree in earth science minor in CS graduating in 2019 and had to touch microsoft for arcgis in one class, and an excel spreadsheet in another.
Like yeah if you have a lot of pre-existing infrastructure migration can be a pain but MS is not in anyway necessary.
As much as I agree with the need for digital independence and the fact that universities (and governments) in Europe are over reliant on US tech, it is not as simple as you describe.
There is a lot more happening in the administrative and infrastructural side of things in most universities that one barely observes as student. So every change needs to take also that into account, the management and maintenance of services and infrastructures that must reliably support thousands of users, with relatively strict privacy and security standards, and their migration.
Will follow up on some of the other threads in here!