There are lots of good reasons to release a mobile app's source, especially if it's a side project. Maybe you don't have time to work on it anymore, and it's not getting the love you think it deserves. Maybe there's a more practical reason, such as taking a new job in a related field and having to remove the app to avoid conflicts (although it sounds more the former in this case).

I'd love to open source one of my iOS apps, but it's a bit of a hack and I'm honestly rather embarrassed by the code!