The people I found liked CoC games the least were the kind who enjoyed big, heroic adventure games. The kind who liked it the most were the kind who tended to want more out of their D&D games than just a decent story, monster-bashing and loot.
The general arc of a CoC game goes like this: investigators go in, get subjected to weird stuff, maybe kill a cultist or something exceedingly normal, do some more investigating, see something they shouldn't have, make some sanity checks, the big monster is revealed, more sanity checks, someone might die, monster is defeated through non-confrontational (ie. standard combat means), the end.
That kind of story isn't for everyone. If you're being true to CoC, there is no battle royale. There is no Sword of Owning Elder Things. Most of the fun of the setting comes from your character being subjected to danger and surviving, changed or unchanged. Getting to live is the real victory in CoC. And for some people, that's just not as fun because it's the opposite of heroic fantasy. A lot of people also hate mechanics like Fear and Insanity because they take control out of the player's hands and often stick them with bizarre disabilities that are hard to make believable. ("You see a Deep One." "I fail my sanity check." "You're now have a crippling and all consuming fear of DAISES!")
It's still possible to kick ass and chew bubblegum in the CoC setting, but done right it always inevitably comes down to a problem the players aren't supposed to be able to handle by direct means. Amulets, mystic rituals, NPCS, there's always something in CoC that's there to help you resolve the big problems rather than straight confrontations...and that leaves some players feeling like they're not the stars of the show, the big bad monsters or the NPCs are.
I personally like CoC and what it asks of you as roleplayers, it's one of the few games that actually inspires some genuine fear and caution in players. But the endings often feel like an anti-climax. If you're not flopping around helplessly in the face of an elder thing, you're on the edge of whatever is happening so you can continue to function in the game. (Ie. killing hordes of cultists while the big bad is awake and going crazy at the center of the compound.) I mean, most CoC stories end with the main character doing the smart thing and running the fuck away.
In the end it always comes back to the players and what they enjoy. Some players just genuinely do not enjoy their game setting trying to scare them, either thematically or mechanically. They don't enjoy feeling like they're not the stars of the show or that they can't take control of the game setting and do things on their terms. On the other hand, there are players who like restrictions, who like that CoC narrows their options because it leads to a more believable-CoC experience. They like watching their characters fall apart and they like a threat they can't simply shoot in the face. If your typical heroic RPG is about player agency and why agency is awesome, in some ways CoC is about taking away agency and why that, too, can be awesome.
For me, I generally like reading CoC novels more than I enjoy trying to live them, but I do appreciate a CoC game now and then simply because it changes the pace of what your average RPG offers you.