Further context: Their org was originally called rackt (a rough portmanteau of Ryan florence and michael jACKson). When Facebook donated the reactjs namespace

Further context: Their org was originally called rackt (a rough portmanteau of Ryan florence and michael jACKson). When Facebook donated the reactjs namespace to the community, they moved it there alongside a bunch of other popular community projects. React Router was the project that taught them React. Since starting it, they decided to quit their day jobs and teach React full-time. rackt (the sandbox of two Internet friends) is now ReactTraining (an actual company). As spicyj said, they probably moved it back to help build brand recognition and use their flagship product to add credibility to their new business.