Because Facebook has thrown tens of millions of dollars towards getting a unified cross platform method of having 60fps rich mobile apps. Because managing an app of more than trivial complexity on iOS and Android is massively expensive. Because this approach offers the most leverage with the least trade offs of performance, development overhead, and future viability.

And because live coding mobile apps with a REPL is epic.

These are all developer centric points. What about users? Android already needs huge batteries, make everything run JavaScript and they'll need to be even larger. And forget computationally heavy apps? The hardware android runs on doesn't exactly have the best JavaScript performance.

I'm not sure you understand what react-native is... The app your users use isn't running javascript, it's not Facebook Cordova. You use javascript to compose the app, there's no javascript in the app you deliver to the users.

Pardon my incredulity, but if you use React, how can you not know that it uses a JS runtime? While it's not as bad as Cordova, you're hardly doing your users any favors in terms of performance by using React.

What? Surely the JS you write is embedded in the release build.

Portability? With a little setup you can write your logic in one language with a reasonably low amount of extra work to handle different platforms. Staffing up two separate teams working in Objective-C and Java isn't ideal either.

I'm guessing the answer to this is: because the problem is ridiculously bad.

People will always suggest what they know as a solution to everything. A lot of people only have deep knowledge of, say, Javascript or Python. That's why you see people in threads like this suggesting these languages as the solution for whatever problem they envision.

That's also why you see horrible solutions for problems that have already been solved in the past.

There should be a rule that says that you are not allowed to design a framework until you have direct experience in developing for at least 5 different systems from different periods in history first.

If a key problem is the need to build every app for multiple platforms, why wouldn't an abstraction layer be a valid approach?

Sure there have been some failed attempts in the past but why not encourage RN? Clearly it's working for many applications and being actively developed.