There aren't enough competent people around, and even fewer who prefer the same workflow as the original author.
What really happens if you open up the code base: Mediocre people who want something for their resume flock to it, work on unimportant issues, add bloat, CoCs and generally make your life hell.
This is a great decision by the author, and the way he states it makes it socially acceptable in the current climate, where hordes of entitled and clueless people have the upper hand over the experienced and productive classes.
The latter part is the real reason why people burn out;it wasn't that much of an issue when you could just tell people to stop bothering you with unimportant issues.
These days it is like walking around in a train station where random people can ask you to carry their suitcases. If you don't politely oblige, they shout "privilege" and report you to the station's political officer.
What really happens if you open up the code base: Mediocre people who want something for their resume flock to it, work on unimportant issues, add bloat, CoCs and generally make your life hell.