It links to https://en.wikipedia.org/wiki/Arch_Linux#Derivatives which indeed lacks any mention of CachyOS. Luckily, Wikipedia is free to register, and you can just edit pages you feel like could be better. Seems like you found the perfect first edit to make for yourself :)

It's an endemic issue on wikipedia, and even editing wouldn't fix this one instance, since someone can (and demonstrably already has) remove whatever you add later on. The issue is wikipedias preference for "deletionism", removing perfectly correct information for no particularly good reason. It's especially pernicious when it comes to short articles, which tend to get deleted with impunity, and redirected to sections of articles, which later get renamed, destroying the link, or removed altogether. Nothing can be done by any individual to fix this issue, since it comes from a wikipedia wide policy, which unfortunately is not one of the things that "anyone can edit".

I agree with most of what you wrote, but unless you can demonstrate that someone actually added CachyOS to the "Arch Linux-based" on the "List of Linux distributions" page and it was later removed, I'm not sure how much it matters how Wikipedia generally works.

I have a long Wikipedia history, but that is not the point. There already was a CachyOS page, and it was removed. Why bother contributing stuff that will just be deleted again?

It might have been removed due to the editor's impression that CachyOS is not significantly different from Arch. With proof to the contrary the page may be restored.

There are a lot of derivative(I don't mean it in a negative way) distors out there, not sure if they all need pages.

Most moderated spaces remove content that doesn't fit the community, Wikipedia does take that to the extreme but I still prefer that than the opposite extreme.