That's my entire point. It's death by a thousand cuts. Now I'm responsible for an IRC server, a web frontend, a mobile app and a bouncer.
The OP said "just run an IRC server". There is no "Slack or just an IRC server". There's "Slack or a number of connected, interdependent services you need to maintain". I'm not saying it can't be done, or that it isn't the right answer for some people, but it's also a lot more work (and thus, expense) than just paying for Slack. It absolutely makes sense that people do it.
That's my entire point. It's death by a thousand cuts. Now I'm responsible for an IRC server, a web frontend, a mobile app and a bouncer.
The OP said "just run an IRC server". There is no "Slack or just an IRC server". There's "Slack or a number of connected, interdependent services you need to maintain". I'm not saying it can't be done, or that it isn't the right answer for some people, but it's also a lot more work (and thus, expense) than just paying for Slack. It absolutely makes sense that people do it.