Superhero comics tend to have too many word balloons.
Look at this mess from Amazing Spider-Man Annual #42. Do you even want to start reading it? There's very little room for the art to say anything in pages like this.
Contrast it with these two pages from Ghosts by Raina Telgemeier, which also have both narrative and dialogue.
The figures in Amazing Spider-Man Annual #42 are so much more rendered and speak so many more words, but they say SO MUCH LESS than Raina's expressive characters in Ghosts.
Yes, these comics are for two different audiences. Two different markets. But the market for children’s and young adult comics is thriving and growing, while superhero comics are struggling to find a way into the readership that YA comics have established.