For me personally, I guess the biggest reason is being able to control the user's experience, as well as my own. Plus I think it's neat, and it was a fun project to do on a Sunday afternoon :)
You seem to completely misunderstand. People using, forking or contributing to your projects do not want their user experience to be controlled by you. They want their own familiar user experience.
Of course it's a fun project, but it's really meta. Wouldn't it be more fun to work on one of your actual projects ?
FWIW, without an easy way to browse the code online or report bugs, I'd currently consider that a poor experience compared to GitHub. Of course that would no longer apply if more functionality gets added...
