Nerds might love Cthulhu, but Hollywood does not love nerds. The Hollywood bigwigs like to make nerds think that they're being marketted to, when in all honesty it's only because they can get the children and normies on board. They're too huge, and their product too high-budget, to really rely on a market of hardcore fans, geek hipsters, and money whales the same way that tabletop and B-Movies can. They need ticket sales up the ass coming from everyone in order to CONSTANTLY GROW AND HAVE THE MOST MONEY or else it's an UTTER FAILURE. Big media corporations only take ventures that offer them ALL OF THE MONEY or none of the money. They'll only pour their millions into things that their marketting team insists is a 100% sure bet for profit.
So why do we have superheroes? Because they're mainstream. Everyone knows Batman, superman, and Spiderman. They've been making movies about them for years until the industry flanderised itself into an all-or-nothing sequels machine. The only reason Joss Whedon, Deadpool, Suicide Squad, the Guardians of the Galaxy, and all those other "obscure" nerd-related things have been brought to the masses as blockbusters if because they're connected to the big names and can be brought into the fold as merchandise pointed at people who aren't really involved in comics and/or have parents that'll shell out cash for them.
Nerds are just an outlier that get pissed off and deliberately pirate and boycott your shit whenever you get something wrong, The fact that corporations can appease that demographic is nice, because there are whales among them that will spend hordes of money on whatever you wanna give them, but honestly we're one of the most fickle, sub-divided masses you could ever want to market to, and taking a big risk like this specifically to exploit the name and concept and grab money would only wreck the already unstable love-hate relationship that the 'nerd' demographic has with blockbuster-making corporations in general.
Among those turn-offs, there's also the fact that Cthulhu is a horror thing, so he can't be marketted to families without being "Neutered". His source material is old-timey and kinda racist, so he can't be marketted to teens without another internet shitstorm. He's public domain, so he can't be made into one universal franchise that you can royalty the fuck out of, and people are just as, if not more likely to buy the well-established fan merchandise rather than your own. And basically, he can pretty much only be marketted to nerds. A wide range of nerds, yes, but only nerds nonetheless. So, if you're going to pour big-budget blockbuster money into this mold, it had damn well better be great, or nothing. And we all know Hollywood has a hard enough time guaranteeing that they'll have an audience, how could we ever expect them to guarantee quality!?