Because I was curious "why", I searched and found this[0] which doesn't sound all that different from the OP examples.

Why create SerenityOS?

When I asked Kling why he decided to write an operating system entirely from scratch, he had two answers. The first, pragmatic answer was he wanted a daily driver operating system for himself, by himself. Other users and developers were welcome, but—initially—they were largely showing up for the ride.

The second answer is that SerenityOS started as a personal therapy project. Kling is a recovering addict, and he decided to build an operating system as a long-term project to focus his mind and occupy his time, similar to the way someone else might decide to build a car or house.

Although Kling still considers SerenityOS to be his eventual daily driver, he's expanded the scope of "who it's for" from "me" to "us"—where "us" includes all the people who have shown up, taken a liking to the project, and decided to pitch in.

[0] https://arstechnica.com/gadgets/2021/08/not-a-linux-distro-r...