Lots of different chat software had easy onboarding & offboarding as well as persistent messaging before Slack and none of it was successful in the same way.
But sure, ok, so let’s hear your theory on why they got big and how it requires all of this client side RAM usage. So what is it?
Mostly what drove orgs I’ve been with from one to another has been pricing (Slack having a free tier ate Hipchat’s lunch, like I said), and “buzz”. Slack was the hip thing to get on in 2013.