I'd say there are certain programmers, who after reaching a certain financial security threshold, would do exactly that. Just as there are people who would happily sail a yacht around the world indefinitely, though it would bore me silly. Is Carmack one of those? Who can say. This kind of programmer can be disguised by the fact that code hermits often make money by accident! When you love what you do, what you do tends to be good.

I have met Carmack before at Siggraph many years ago and I can say that he struck me as someone who was a 'Code Troll' because he loved it. That he made money was great, but I think he has such a deep love of the technology for technologies sake.