For me, it's about the journey, more than the destination, but I still like completing all my projects. Part of the joy, is watching my work being used (and, sometimes, abused) by others.
It’s difficult to do this when there’s belly’s to fill.
Of course, don't do open source if you don't enjoy it - because I doubt the time spent is optimal for getting the most money, but if you do enjoy it then it can very much help increase your income indirectly.
It is not hyperbole to say that some of the software I've written has saved many lives. Others tend to use a lot more hype to describe its impact than I would.