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.
Vim was one of the first pieces of software I learned when I switched to Linux in college. It was tricky at first, then it delighted me to no end. It remains a daily part of my life nearly 20 years later, and I'm still learning more about it every single year.
I can't count the number of times I wish I could drop out of insert mode in normal web browser text boxes.
Bram's insistence of donating his earnings to helping the children of Uganda is also incredibly selfless, and it's impossible to mention him without bringing this up [1].
We'll miss you Bram. We'll be learning from you for decades to come.
You can, if you really want to:
The number of people who spent that much time working on Open Source is very small, and the number of people who have spent that much time purely in their spare time is smaller still. In fact, I don't really know of anyone who even comes close to Bram.
The number of people who spent this much time volunteering for anything is very small.
Bram's effort on Vim was phenomenal and exceptional by any standard.