Ask any accomplished Mac OS X developer why they do what they do, and you'll likely to find that the reasons are as much personal as practical. They want to enjoy themselves, and they want to make things people will like.
Writing Mac OS X software with Apple's Cocoa environment is rewarding, but it takes some time to get good at. Tree House Ideas offers tutorials and one-on-one mentoring for Cocoa developers.
Once you have an application, you'll probably need some design work. We do that too.