You just hit the nail. Yes, of course this makes much more sense if you are working with open source and you know your works helps you, your customer, and countless others that you even don't know about. How do people NOT working with open source keep up? I don't know, probably that's why they want to move on to something else.

And also, being a programmer in open source or free software is not only the programming, its also the community and bonds you make while contributing.