> I wonder what personality trait in us programmers makes us willing to work without compensation on our free time and why it doesn't seem to be present in artists

I don't think it is much more prevalent in programmers than artists. (That's why I also think that the 'show me your GH profile'-style recruitment is shortsighted; most of the best coders I've ever met (who I consider geniuses, really) had no OSS contributions at all, they just make boatloads of money at bigcos (Google, MS, fintech)).