I work as an IT management professional for a fortune 500 company during the day, as a full-time parent of two young children in the evenings, as a graduate student (at least for a little while), and as an author when I can. Of course, maybe that is why I'm not very prolific. Throw in the weekly tueday night game and a chronic addiction to NWN and scripting development and its easy to see why the grass is so high. Mix in shabbat observance and... well, you get the point.
It is hard to imagine anyone could write for a full-time living, especially if they had kids.