EmberData, Ember Routing, Ember Multi Applications (can't remember what its called, but its a precursor to microfrontends) all in one CLI tooling etc.
I could never understand what holds Ember back from being more used. I think it used to be performance but I think they addressed that with Glimmer many years ago.
It's not being used more for the same reason Ruby on Rails is not used more.
Both are batteries included frameworks, with a much steeper learning curve than e.g.
<script src="https://cdn.com/vue.js">
Plus people like to tinker and wire up things together themselves, like router, rendering, state management, testing, etc. That's more exciting than `ember new project`.
I was like that 10 years ago too, but now when I learned the ropes I just want to focus on shipping and providing value, rather than wasting my life wiring up 17 javascript packages of the month together.