Teams won by being good enough and bundled into O365. There's probably some value in making a product so available that people can use it where normally they wouldn't have the opportunity.
I was going to comment that teams doesn't have threads and slack may still win long term, but turns out teams added threads in the last couple of months(1). So yeah.
I'll vouch for this. I moved from Slack to Teams and Teams is clearly an inferior product. That said, I don't think SalesForce owning Slack is really a big improvement.
