> and the number of people who have spent that much time purely in their spare time (i.e. not as part of their job, like Torvalds or van Rossum) is smaller still.
I agree, but the fact that there's a non-zero amount of people doing it shouldn't be overlooked. For example maintainer of qutebrowser (who also happen to be in pytest core team) and apart from a teaching job at an university a couple of months per year, he's working full time on OSS. The main characteristics they share (at least those I met) seem to be a deep love for the craft, a deep love for people, and be virtually unfazed by the amount of money they can make if they weren't doing that.