Instant Messengers like Google Talk, and Group Chat apps like Slack come and go along with their walled gardens, but IRC just keeps on keeping on.
IRC is legacy tech that kind of sucks, but all improvement has been done by startups rather than open source developers, so we have a fragmented mess. I mean, XMPP exists, but it's not that great either.
It turns out UX is more important than whether you need to convince people to install a new piece of software for the vast majority of people.