My company is already paying for Teams as part of our O365 Installation. We won't use it, simply because of the network effect the Shared Channels have created.

We have shared channels with Integration Partners, Suppliers, Enterprise Customers... These are extremely valuable ways of communication once setup, especially with simple file-transfer thrown in, etc. Leaving Slack would mean slamming the door in the face of these entities, something we're simply not ready to do for the cost-savings that ditching Slack would mean.