Earlier quoted context omitted.
Except when you have to manage it yourself and something breaks or the infrastructure you have to manage needs managing.
See the comment above. If you're using Slack to avoid managing infrastructure, there are plenty of great (read: open source) alternatives. Even if IRC isn't for you, there's XMPP, Mattermost [0], Let's Chat [1], and Zulip [2]. [0]: http://www.mattermost.org/ [1]: https://sdelements.github.io/lets-chat/ [2]: https://github.com/zulip/zulip
Just to add, you can use IRC clients to connect to Mattermost https://twitter.com/mattermosthq/status/668898122630721538