Sharing doesn't necessarily mean someone cloning or contributing to your project. I find github useful because it lets me read other people's code both for evaluating potential co-workers and getting better at my craft.

I've learned a lot from reading other people's code and I still think it's one of the best ways to learn new languages and techniques.

Even with some of my more obscure projects on Github (like a ZNC module that sends IRC notifications to my phone via Notifo) have garnered some observers, forks, and pull requests with features or improvements that I probably never would have gotten if it had either been on my own repo hosting.