Adding ancient eldritch gods into Fallout, with such large and sprawling plot lines was a huge mistake.

People will say, "Yeah but what about the ghost in Fallout 2?" Yes FO2 had one side quest with a ghost. It was a one off, with no huge backstory propping it up, it wasn't constantly revisited. It didn't change the whole vibe of the world. It was one side quest that made you go "Huh that was weird." and was quickly pushed aside.

In comparison, including eldritch horrors in a front and center way, with quests like the Cabot questline being the most egregious. There is also the Dunwich building, the Dunwich mine, the cult and eldritch creature in FO76, and more.

Any one of these, one their own, as a one off isolated thing might be alright. The Dunwich building especially works as a weird unexplained oddity. It is the dose that makes the poison though, and now there is so much Lovecraftian stuff packed into Fallout that it has changed the texture of what Fallout is. The more the Lovecraftian stuff is added, the more of the original "an apocalypse of our own making" 1950s militarist, corporatist setting gets diluted.