It's common startup knowledge at this point that a splashy launch will always lead to subsequent declines in usage, because huge numbers of non-ideal users are attracted by the initial press event.
The viral growth you're talking about pretty much never occurs after a huge launch event like this, and is reserved for more methodical releases and/or lower initial starting user counts, e.g. Instagram testing Stories, Facebook growing from college to college.
The viral growth you're talking about pretty much never occurs after a huge launch event like this, and is reserved for more methodical releases and/or lower initial starting user counts, e.g. Instagram testing Stories, Facebook growing from college to college.