Comics have inaccessible art styles. There's often too much clutter, too much going on, not enough symbolism or abstraction. Manga and anime have simple linework, competent colouring (or black and white).
Go look at Detective Comics #1026. Beautiful art. Varied lighting, colouring, all sorts of perspective shots and action shots and detailed backgrounds. It's complete garbage, no kid is going to want to read it. They're going to go crosseyed trying to process this masterpiece. There's too much visual information.
Compare to this random splash page I found in a recent chapter of Dr. Stone. The backgrounds are speedlines, the paneling is cramped, the anatomy is cartoonish. But everything is so much simpler and easier to read. Forget a kid - an ADULT is going to have less of a headache reading manga than trying to concentrate on a comic.
In short, the beautiful, meticulously-coloured art that comics have? Holding them back. I never hear newspaper comics complaining about how they're "dying", at least not nearly as much as DC or Marvel. And newspapers aren't exactly doing well.