Slack is, I think, mainly focused on the messaging and relies on third parties to integrate other features. Microsoft is a behemoth that wants to sell their complete software suite and tries to integrate all of them together for a "seamless" experience. They do have an incentive for their own products to be good and used instead of third parties.

Plus once they realize how much data is in these wikis, they will want to ingest them for AI (if not already done), so there is an incentive for them to have more users on their solution instead.

Edit: And even if the OP is not relying only on MS for sales, they still depend heavily on them and their App Store. They are not competing with Confluence or other systems, they are competing with Teams itself.