I think the Marvels did poorly in particular because of the fact that it's a team-up of three superheroes, two of which were introduced via Disney+ shows. One of those shows (Ms. Marvel) was the worst streamed MCU show by a landslide, and the other show (WandaVision), the Captain Marvel in that (Monica) was a side character, so some people may not remember her character very well and may not remember what facts they're supposed to know for the movie to make sense.
I think, in general, Disney has been trying to make all the other things feel like required viewing so they get those huge numbers like they did in earlier installments of the MCU, which only the most diehard of fans are going to do these days. Other people are just going to pass on all of the content. Like, I'm not going to watch a Disney+ show or a different MCU movie about a superhero I don't even care about just to fully understand the movie about the one I do care about.
For the DC, they haven't had a coherent vision in years, so tbh, it's more surprising when they have a superhero film that does well than when it does poorly. And even then, their films that have done well (Aquaman) haven't exactly been lauded as cinematic excellence.
Plus everything
@seungfloral said. I think people are just past the point of being interested in spending theater prices to go see a B or C or D-list superhero in a film that is going to feel vaguely familiar to the literally dozens of other superhero films that have come out in the past couple decades. But you know, maybe Madame Web will make a billion dollars next month and I'll eat my words on that.