How do you go from a billion dollar film to grossing less than the Flash? I've never seen a bigger collapse between two films like this.
The way I see it there are definitely multiple reasons that have resulted to this.
The movie obviously doesn't resonate with audience and critics and that's hurting opening weekend and is going to kill its legs even further in the following weeks.
Like others have said, the name of the film and lack of marketing from the actors' side probably hasn't helped, though at this point I don't believe it made a huge difference, it just pushed it even further down the drain.
But I think a very important factor in all this is that people vastly overestimated the character's and first movie's appeal based on Captain Marvel's gross. Like I said before that film undeniably had a major push both from the Endgame hype and from it being the first female led superhero film in Marvel, coming also after a big hit of the rival studio's, Wonder Woman as well. But the movie itself feels like one of the least memorable entries in the MCU from everything I've heard and seen from fans, critics and general audience.
They obviously made a big mistake when they underutilised Carol in subsequent appearances in the universe as well.
But of course even so, the biggest issue is not with her, it's with the brand. The quality of the films has dropped, the quantity is overwhelming and there doesn't seem to be a coherent plan and a tight ship like with the Infinity Saga. Feige became cocky and thought they can make money out of every single superhero in existence and that the multiverse gimmick of returning actors would be enough to keep people flooding in cinemas for a few more years before the X-men arrive.
There's definitely a fatigue in the genre and there's a fatigue in Hollywood tentpole movies in general. That's not to say that there aren't or won't be successful examples in each category in the future, but in the age of streaming and a post-pandemic world the days where almost every mediocre comic book film or blockbuster was attracting the masses seems to be over, at least for the foreseeable future. People want familiarity but they seem to also want new spins in things they know.
This movie year has been a very unpredictable one and while this is kind of a shocking decline, it's not out of nowhere and there have been signs in the past couple of years. Again I feel bad for the director and the actresses but I choose to look at this as a positive signs for better things to come, both in superhero films and Hollywood blockbusters in general. Monopolising the industry hurts cinema as a medium. It's when you fall that you start becoming creative again, so let's hope that some of the right lessons will be learned this time (breaking out of the formula, greenlighting different things) and not the wrong ones (making fewer female centric films).