However, the reason for this wasn’t so much MS being evil as Google and others basically ignoring sensitivities about where user data is hosted. MS guarantees (well, sort of) user data is stored in the EU when customers set it up properly.

No one else does (or did, maybe things have changed by then).

So the monopoly MS has here is basically because they do what their customers want them to do.

Of course they never considered any open platform like Jitsi that did not require an actual account

Jitsi was hosted by a few teachers who voluntarily managed all this infrastructure for schools in my state (Germany, BW). They didn't have enough servers since there wasn't much demand until the pandemic. These scaling problems meant only teachers could use their cam (which most students were quite happy about).