See, I don't even think it's marketing, it's Google not understanding what they already have and engineering a solution without a problem. Hangouts as an app on mobile is okay - I have qualms, but it works well enough. Hangouts on Desktop though is horrible, and it's integration into Gmail is frustrating at best (it took them a long time to get something as simple as status messages back to Hangouts after the switch). I get the impression Google saw what was happening with Slack and wanted Hangouts to be that (and also a successor to Wave); a persistent "better than email" communication method with every bell and whistle you could want for communication. But since Hangouts was released, they've removed the few fun social features, removed hangout plugins, and just took what was feature-rich and dumbed it down to the point where I wonder why I should have an entire separate page open dedicated to hangouts when even Skype is a more graceful solution with more functionality.
I really liked gChat when it was small and out of the way. I won't make the claim "everyone used it", but we certainly enjoyed in our GAFE environment as it was an appropriate intermediate between email and phone call.
Duo makes me ask the same question now - why do I want this as opposed to just Hangouts, unless video is going to be removed from Hangouts or only Duo is going to get improved performance updates. This seems like it could easily be a hangouts update instead of a standalone application, and Hangouts is already available cross-platform on iOS and Android, or via any modern web-browser.