Julio Merino:
One reason for this choice is NetBSD’s build system. Once you look and get past the fact that it feels frozen in time since 2002, you realize it is still one of the most advanced build systems you can find for an OS. And it shows: the NetBSD build system allows you to build the full OS from scratch, on pretty much any host POSIX platform, while targeting any hardware architecture supported by NetBSD. All without root privileges.
Good insight into the NetBSD build system, and how to use it to cross-compile a
custom image for a Raspberry Pi. In particular how it achieves unprivileged
builds without tools like sudo or fakeroot is quite neat.