I think a great example of the struggles that cause people to abandon Ember are shown in posts like this.
It’s a fairly simplistic action, but Ember (or at least the community) doesn’t seem to have a good answer for how to handle this. The downside of opinionated frameworks is that you spend more time having to document, explain, and support those things that fall to the edges of the opinion. The above blog posts references one of them. And it’s a case where routable components aren’t going to help either.
The community does more to address these issues, the more people will stick with Ember.