I'm sure this is just Microsoft unifying everyone on the same comms platform, but seriously, I don't know anyone who chooses Teams.
I know non-tech folks who chose Outlook 365 because of familiarity and then end up on Teams because it's free, but there's a difference between "I chose an email/identity platform that I know and I guess I'll use its chat app too" and "I evaluated team chat offerings and Teams is our top pick."
Hell, at my most recent company (which was founded on O365 before I arrived) I replaced Teams chat interface with self-hosted Mattermost (Slack's HIPAA-compliant tier is way too expensive for a startup) and it was roundly loved. We did still lean on Teams for its video chat, because most of our non-tech staff know how to schedule and join video meetings, but even then the top complaint I got was from folks on Windows laptops whose Teams plugin for Outlook somehow got corrupted (or something?) and suddenly Outlook's Teams integration was gone.
Just an awful product all around -- said with no offense meant to the team building it.
_Update_: I now notice the text "for the sole purpose of video conferencing" which lines up with my use case, but still -- of all the video apps I put Teams down with Webex as "bottom of the barrel choices" due to the constant performance and functionality issues.