That is indeed the question, and I too haven't found an answer (hence my post). I hadn't thought about the connection with sports, but I had only tepid interest as a kid, and have never been especially competitive. I've also never been especially motivated at much of anything, so maybe there is a connection somewhere....
It's funny to hear the lawyer describe himself as unmotivated. I think competitiveness is a big factor. There is a breed of human out there that really gets off on being better at a thing than someone else. Not from being good at something, but from the comparative 'Better than X at Y.' I think that type of person derives a lot of satisfaction from practice, because it's a known way to beat the living tar out of someone else.
Haha, well, I didn't work especially hard in law school (and my grades showed it). I suspect there's something to the competitiveness thing, as I said somewhere in this thread (I think), but I'm not sure how that plays out in this context.