That's been within the last year I think - I too have been using Linux and Firefox for calls in Teams meetings from 2020 to last year when I had to move to the Teams Linux client (which they're deprecating, so having to move to Chrome or Edge).
So this means that I pull my customers into a competitor product, and they also get to hear me badmouth Teams if I find an opportunity to do so.
Teams doesn't have to be better, they're just bundled.
It's better than where we were (Cisco jabber) but also worse than what's out there.
Absolutely a monopoly maneuver.
and didn't really maintain for at least the last 2 years either
(it basically ran a often very outdated version of the web app + some AFIK unnecessary and buggy custom audio handling)