Chat is a commodity. Right out of the gate, that's not great for margins.
Enterprise chat might not be a commodity quite yet - SSO, DLP/data classification, auditing, retention, compliance checkboxes - but these seem insurmountable at first glance to get a FOSS solution to reach a viable enterprise feature matrix.
Killer features as a moat might help, but while almost everyone uses chat, everyone probably uses chat differently, so that means discovering killer features for a niche and trying to own that segment before expanding. Unfortunately this is the "Draw the rest of the owl" part, because while I have quibbles with chat apps, I struggle to envision a chat app that does something radically different than any other chat app.
If you built that alternative, would companies choose to use it? they get teams built into their outlook and office 365 contracts and all the other integration. Slack didn't lose because it was worse, so just being better isn't enough.
The hurdle is producing a full suite covering everything Microsoft sells in one package, which seems impractical without their funding to start with.
What is it about enterprise IT that is preventing us from building a better alternative?
How can we get around those hurdles?