You cannot compare an open chat, with a strong interest in a particular topic vs you team's Slack channel.

Online games work well, because you have a visual and full engagement.

Compare that to work communications... You are totally async on slack, it's just a simpler version of email at this point. Just because people are online in Slack today, doesn't mean that they'll respond within minutes.

If someone is online playing a game, you know that they're there. Old IRC was pretty much the same.