Why does Cthulhu Mythos implicate HP Lovecraft, and why is HP Lovecraft a character tag and not a copyright tag when it's being used in this manner?

https://e621.net/forum/show/18897
This has been brought up before, I don't remember what happened with it and I'm a work right now so I don't have time to read through the old thread.

Didn't go anywhere. If the Lovecraft tag exists in this extent at all it should be a copyright, but I don't really think it should exist like that, either, as the Cthulhu Mythos includes many things not made by Lovecraft himself, such as Hastur, the Hounds of Tindalos, and so on. It should just be used as a character tag for the man himself.

Yog-Sothothery is the name Lovecraft used anyways.