As someone that ran a company while working on side open source projects, don't underestimate the therapeutic value of writing code. (As a CEO, my job had almost no coding, and working on my opensource projects made me happy, and restored a lot of my energy.)

CTO and lead developer on a focused project are very different jobs - my guess would be he relaxes from the very strategy and soft-skill heavy day job by diving into a challenging problem that keeps his dev chops up and lets him focus on a finite problem.

So working a shit ton then.

No idea on Evan Wallace's perspective but there is a possibility that it isn't seen as work. It would like be me solving sudoku or some of my friends building LEGOs or solving extremely hard jigzaw puzzles

I understand that because it's often how I feel when I'm doing programming work. However, I would still consider that time spent working.

To echo what others have said here, my role as CTO and now CEO has gone from 95% coding to about 5% these days. So some nights I code on ideas and things that have been swirling in my head, just because it’s nice to just quietly write code and solve a finite (but possibly difficult) problem without interruptions. It actually IS therapeutic.

Same

The tool is likely helping Figma pretty directly by cutting developer build times.

Maybe there's not much to do as the CTO of Figma. Throwing time into Esbuild doesn't mean he's neglecting his CTO duties.

In which case my last option would be relevant:

> or his output is actually not as high as it looks

Frankly most of us would not be able to create esbuild even with all the time in the world.