The Ember community made a proactive decision to abandon StackOverflow around the 2.0 release (about 2.5 years ago). StackOverflow simply does not provide the tools we needed. For example when you answer a question: Are you answering for version 1.0 of a library? 2.0? Perhaps the "correct" answer for each is different. Perhaps, over time, an answer that once was correct is now suggesting something deprecated or not in line with best practices.
StackOverflow doesn't provide any features for dealing with versioning and changes in what is correct over time.
If your community has a StackOverflow moderator, perhaps you can update all the answers you want on a regular basis. I don't know, because our community had no such person, and the StackOverflow team was disinterested in helping us come up with a solution (the Ember project reached out).
Additionally as a tool matures (Ember is over 5 years old) you take more of this stuff under your own wing. Ember has a robust set of companies offering video training, in person training, and books. We have a community chat, a forum, and very active meetups. All of these things are controlled by members of our community, meaning they can respond to changes more fluidly than StackOverflow (moderated by some people outside our community) ever could.
StackOverflow just is not designed for long-lived multi-versioned software. So guess what happens? Users of that software don't stick around on StackOverflow. For living projects the short-term trend will almost always look better than long-term trends.
Ember's story here is not universal. I'm glad there are developers finding StackOverflow useful for other libraries. I think the story StackOverflow should tell is one that focuses on what they do well. But to draw a meaningful lesson about the JS community as a whole from such a idiosyncratic data source is a fools errand.