Why? React and React Native are both pretty core to Facebook's main applications these days (all of Instagram is written in React, there's a smattering of components all over the main Facebook page, and multiple Facebook-written applications are written in React Native, including parts of the main Facebook app). In contrast, Parse was more of a dev-infrastructure product that didn't end up impacting developer relations as much as Facebook wanted it to (I'm guessing)

The thing is it was not just 30 minutes. Between the built-in push notifications, admin console, great geo support, and easy scaling it was a complete godsend for building MVPs in a reasonable amount of time. It will be missed by many, many independent developers & consultants.

The major difference though is that react is a self-hosted open source library. Yes, Facebook could drop support for it, but there are enough people using it now that it would probably see community updates for quite a while.

I'd be hesitant to use anything released by a large company that they don't use themselves for their flagship product(s). Angular 1 comes to mind.

I believe Facebook does use React for facebook.com, but not React Native for anything in production yet.

Libraries can always be forked. Services not so much (though in this case you should be able to self-host, but that's not always the case)