It’s like Linux From Scratch… with friends. Every distro has a purpose. I haven’t done super niche. One day I’ll probably try to run Gentoo much more seriously, and maybe an LFS just to see if I can.
Linux is the realm of all computer science students when it comes time to learn about operating systems, processes, threading, interrupts, schedulers, memory, etc. All levels exist in this space. The major distros all have underlying reasons they exist too. It is not branding/marketing like much of the consumer world.