I don't think Microsoft would buy Slack given the money they've dumped into developing and promoting Teams. Seems they're too far gone at this point.
Disclosure: Work at MSFT, not on Teams.
Disclosure: Work at MSFT, not on Teams.
They bought Github even though they already had VSTS aka Azure Devops that offered free git hosting and they just abandoned their own browser engine for Chromium. Also they bought Xamarin.
Microsoft would buy to prevent someone else from doing so.
Though its hold has weakened greatly, the Outlook, Exchange, and AD behemoth still own enterprise communications.