alt Hacker NewsBack in the day you needed a bnc if you wanted chat history. The mobile experience has been abysmal until very recently.
Also when discord came out there was a certain appeal to having voip built into the same app, and not having to maintain a separate vent/mumble/ts.
The voice thing always sneaks up on me as a requirement, because I never, ever personally want to use that. I'm not saying it's not a good feature, just one that doesn't occur to me. You're probably right, though.