[AstralStorm]

The real question is: why buy Slack when relatively equivalent solutions such as Mattermost or even Discord exist?

Seriously, the only thing that could convince a company is either lower admin cost (vs Mattermost) and way better customer service when something fails. (vs Discord) Pretty sure big co mc corp wouldn't like a potential competitor running its comms.

Additionally a strong competitor is as always email. Perhaps enhanced with scheduling and mailing lists. If you don't like to set it up, you could pay Google for example. And both Google and MS are improving their chat/IM offerings.

They can and will undercut such a start-up instead of buying it, unless they see enough value in an acquihire.

[owenwil]

Because with Mattermost or Discord you have to maintain it yourself, and their tooling isn't very good?