The Marvels is the next movie from the Marvel Cinematic Universe, but despite its name, it's not projected to be a major moment in the shared universe. Promoted as a sort of light, airy affair, this less-than-pivotal nature is likely a big part of why the movie's box office predictions are so low. This suggests that concerns over "superhero fatigue" are legitimate, though there might be something more to it.
Source:https://www.cbr.com/the-marvels-box-office-predictions-superhero-fatigue/