So what about the mobile device issue? Corporate logins?
If you want to match what Slack offers you aren't just running an IRC server, you're going to have a small fleet of dependent services that, added up, just about match what Slack does.
Is it really that surprising that people just opt to pay for someone to deal with all of this for them?
At which point you're not looking at IRC as a service anymore. There are different niches served - but the question was about the reasonableness of setting up IRC alone, which is still dead easy.
If you want to match what Slack offers you aren't just running an IRC server, you're going to have a small fleet of dependent services that, added up, just about match what Slack does.
Is it really that surprising that people just opt to pay for someone to deal with all of this for them?