Right, but HPL never really explicitly included just about anything the CoC games focus on (and half the stuff is Clark Ashton Smith or other HPL neophyte inventions anyway). Most of his "Mythos" takes place in the background so it makes sense that you'd create your "Monsters" based on what you've got, which really isn't much, and then add and elaborate.
That said, sure. Is it lazy for scenario authors to overuse this trope? Of course. But that should go without saying. Any trope if leaned on too heavily is bad. But the story the darn game is based off is centered around cultists. They don't have lines in the story, but they are at the heart of the story. I know I personally walked away with the cultist imagery as my greatest take away beyond Cthulhu himself after my first read.
Alsoplustoo: I can't leave without mentioning this: If chases are new to the rules, don't you think they deserve their own chapter? It's a pretty solid mechanic, and complex, so I personally am glad it isn't just a couple pages long. Conversely, I never bothered fully reading (beyond my first read) or incorporating anything specifically from De Rerum or the flavor chapters like "Mental Disorders" and think the Sanity chapter in 7e is much more concise and helpful.
I suppose if you're reading CoC for the first time with 7e, it's possible you think it's an action game...if you're selectively paying attention to what you're reading? Sorry, dude. I just can't agree. My current main homegroup are all new to CoC and I guarantee none of them would tell you my games are "action packed" and they're ALL 7e since 7e came out. *shrugs*