That's not how I remember it. I remember Slack being more or less functionally identical to HipChat, but HipChat had some PR disaster about their privacy policy that spooked the valley and "switch to Slack" became the wisdom of the day.
HipChat was god awful. It was half assed in almost every way (especially the mobile app). Atlassian simply didn't see the opportunity.
Slack was leagues better. It was as simple as that.
https://www.atlassian.com/blog/archives/hipchats-terms-servi...
Na, they did. They put everything in to Hip Chat, even attempted a re-write which led to Stride, it's replacement.
Check the logos on the bottom https://www.pubnub.com/what-we-do/. The core part of any chat client is? messaging. Outsourcing your core layer, hmm...
Something must of gone drastically wrong somewhere from having it as the #1 business priority and beating Slack to instead selling their customers to Slack.
Slack launched in August 2013.
Stride was release in September 2017.
But then it was way, way too late. 4 years is an eternity. Even Microsoft Teams had come out before Stride (in early 2017).
Slack would go public less than 2 years after Hipchat/Teams launched with $400mm in revenue (FY2019). To give you a sense of Slack's scale and some perspective, the same year Slack went public - Atlassian did $1.2B in revenue.