If you are building a platform for web dev, it’s better to be able to control your technology. Any change FB makes to React may leave you scrambling to patch your tech. Or What if one day FB decides to stop supporting React, or they make a design decision incompatible with your business? While it sounds unlikely, it’s bitter pill to swallow from a business angle.
And then you would probably be forced to support classic FB React for customers that didn't want to migrate, and forked React.
The real issue is if you build any special sauce on top of React. Say you went all in on providing a customized React.Component that worked like a React.Component, but had your platform's logging, perf metrics, etc built in. Then React comes out with hooks and functional components and then you are stuck trying to reimplement your special sauce using these. Or you have to tell customers, "we only support class based components." While functional components are old, FB has shown it will introduce paradigm changes into React, and you are left holding the bag when it comes to supporting them in your platform. And if customers saw a new React feature previewed yesterday, be sure they will be asking for support for it today. FB isn't likely to hand over React to Apache or any sort of open governance model, so changes can be easily made without a huge amount of forewarning, or even a business relationship. Last time I checked FB wasn't selling support contracts or partnerships for React.
