I suspect it's because he's so successful at spawning developer communities around the software he writes. Just look at sway: between 1.0 and 1.1 he was nowhere near the largest contributor. I'd guess that means a lot of time to work on other projects.
@Sir_Cmpwn do you have some insights to share on this? What are the conditions that make you most productive, and what conditions make you the least productive?
I get a lot of help. Fostering a healthy and happy community of contributors in each of my projects is extremely important to me. I'm also able to be more productive myself thanks to the support of hundreds of people who donate to my work or buy a sourcehut subscription, which allows me to work on free software full time.
