[throwaway3306a]

People use Teams because it's well integrated into Office, 365, Entra and other MS products, they would (and recently do) pay for it. It has functionalities that no other alternative has, e.g. it can act as a full call centre solution through a SIP gateway.

[digging]

"Well integrated" is honestly a stretch, but it is fair to say it's integrated with no extra setup.

[throwaway3306a]

How to manage Slack access control via Azure AD groups? Even the most basic integrations are missing in other options...