And its not like they aren't other options. Scott Pilgrim and Crossed were both hugely popular in their heyday and were completely divorced from the capeshit market.

But the industry never followed up on that, or tried to capitalize on it (besides the Scott Pilgrim movie/game but that's a different industry entirely), so it never went anywhere. They were committed to the superhero genre completely. Even the non-super stories still share a universe with those so they are still connected to them.