The main reason why mobile developers get enticed by the cross-platform development capabilities of frameworks like React Native, is, of course, the ability to share code across platforms. A smaller, but no less important reason is the ability to build, debug, and refactor faster. Last but not least, such solutions often help broaden up the variety of tools, beyond the ones dictated by the platform vendor.
UPDATE Feb 17th, 2018: Though not a part of this article, it is worth noting that Facebook changed the licensing of React Native to MIT yesterday. This should come as a relief to many and would certainly increase the library’s commercial adoption even further: