> It may surprise you to hear that the Components library I’m describing is not React Native, but a separate project.
> Why the distinction? It’s simple: React Native hadn’t been invented yet when we rebuilt News Feed in Components. Everyone at Facebook is excited about the future of React Native, and it’s already been used to power both Mobile Ads Manager and Groups.
> (from http://www.objc.io/issue-22/facebook.html)
(I work on React.) We're going full steam ahead on React Native, but this is a slightly more mature project and we figured it made sense to release it for people who (for whatever reason) can't or aren't ready to adopt React Native yet. ComponentKit is also more mature and powers the most important part of the Facebook iOS app so it's virtually guaranteed to be rock-solid, whereas React Native has only been used in production for a few months.
For example Google has many many competing data backend projects build on top of Big Table, emphasing different requirements.
I think it’s quite amazing what Facebook/Instagram are doing. They are creating a legacy that will hopefully inform what Apple and Google do with their frameworks too.