Some of the reasons are

• Community - React Native community is very active and big. When my app got rejected by Apple for some weird reasons, Community was helping a lot to find the root cause of the problem. Even many core contributors contacted me personally and resolved the issue.
• Gradual learning curve - Not steep like any other technology
• Packages - React Native have lots of packages. Mostly You will be able to find a package for all the common tasks. Even if you can't find, It will be very simple to make your own package if you know little bit of Java and Objective C.
• Background - React Native is created by Facebook and NativeScript is created by Telerik. Obviously, More people will believe Facebook than Telerik.

Few months back, I have answered a similar question in hashnode. You can check the answer to know more about my opinion about the NativeScript and React Native.