Because Dart is similar to JS, easy to learn, and better in regards to performance, tools and security. JS is a mess, just look at the equality operators and the fact that you can manipulate classes like String, etc...

The release version runs native code, so is faster and uses less power.

I don't know.

Seems like astro-turfing to me.

Dart isn't much better than JS (as TS or Reason are) so switching doesn't give you too much gains, but a smaller eco-system.

Also, the canvas approach of Flutter feels kinda backwards.

I think it's artifically hyped by Google.

React will be much simpler with hooks and the RN updates will improve native inter-op.

But yeah, that's just my take and I'm often wrong with predictions xD