First, I think you're overestimating how much you can make as an engineer in SV. It's more, but it's not fair to say $100k is "not even close".

Second, there's more to life than working at, say, Facebook/Netflix/etc for money. The pure happiness of working on something you care about is worth a lot of money to some people.

Third, if this person ever wants to get a real job, the $100k won't go away, and they'll easily add $50k to their starting offer for running a prolific open source project.

Lastly, look at that graph. It's going up. Zero to $100k is really good for 6 months, and in another 6 months it'll potentially double. Most startups don't get to $100k this quick. More people will use this as time goes on, they can start new projects, they can do high-end freelancing for companies using it, etc.