I'm not in anyway connected with FB, but I think the reason why React was licensed under MIT more quickly than React Native is because of that licensing environment. Web frameworks traditionally have very open licenses, but native seems more more restricted such as with Qt and the C# thing I don't remember the name of.
Except the largest 3rd party Objective-C and Java (Android) libraries are usually MIT as well. I don't really think this has to do with traditions as far as per platform licensing goes.