My current company uses Slack as the main messaging app, while still using Teams as part of the Microsoft package, for its integrations with Outlook and conference hardware and software. And this is a recurring pattern I've seen in other places. Teams is nowhere close to being a usable alternative to Slack.
Interesting, but isn't it just because Teams is bundled and integrated with MS Office? I couldn't find any specific stats on revenue or how many businesses actually choose to pay for Teams specifically.
Yes, AFAIK you can't even buy Teams separately, it's only bundled with MS 365. The DAU numbers, however, correspond to people actually online and using Teams for communications, so it doesn't really matter (if we only care about "how many users are using what").
Microsoft pushed Teams onto my personal Windows PC in a recent update, as a startup item. And, as far as I could tell, automatically logged me in to my Microsoft account on it.