Here's one: Microsoft management heavily incentivizes their developers to use LLMs for virtually everything (to the "do it or you're fired" level) and the LLM (due to its training data or whatever) is far more able to pump out code with React Native than their own frameworks. This makes it the right choice for them. Not for the user, but you can't have everything.

I don't have any inside information; I'm running with the hypothetical.