I think the hope of projects like these is partly to try to advance interest in Swift which draws in more users who then help contribute to making the language

I think the hope of projects like these is partly to try to advance interest in Swift which draws in more users who then help contribute to making the language more cross-platform, and partly to be f1rst in the project's niche when the language finally crosses that barrier, so that it becomes the de facto standard. (Think Compojure for Clojure, in the same problem domain.)