Ember is made by folks who work on / for small and medium companies[1]. They don't have the build infrastructure Facebook does and are able to create an anointed solution in Ember-CLI because they'll use it daily. React is stuck in a place where the environment it's developed in is unique from what any other user will see. It's difficult to solve a problem when you're not in the space.
EDIT:
This leads to things beyond CLIs too. React is still billed as just a view library instead of a solution for building an entire app. There's no official path from view layer -> complete app (no guidance for data flow, how to communicate with the server, server side rendering, routing on the client).
I think the React team needs to take a little more responsibility for the eco-system it created. You can't call it just a view library when most use cases use it to develop entire applications. You have to provide more guidance, you can't fallback to Facebook not using it that way as the default response. In my opinion most of the Great Javascript Fatigue of 2015-16 was caused by users trying to fill in the blanks left by the React team and producing one solution after another (and quickly abandoning ship as something iteratively better was released).
1 - Tom, Yehuda at tilde.io