Had to try out Teams at work recently, because the corporate IT wants us to switch over from Slack. I'm working in operations for a daughter company of corporate IT. Tried it. It's a joke compared to Slack. Horrible UI and calls dropped all the time, combined with 90s quality. In the case of an incident (I work remote) I cannot rely on Teams at all.

So, maybe some of the microsoft employees feel the same about Teams, and that's why they still use Slack? Interesting though.