A more likely reason why DC and Marvel won't really go after more female audience
It's because the female audience most likely to try out any of their books would want the stories to be stand-alone, present plausible characterization and continuity, and the Big Two in their current state would rather obsess themselves with publicity stunts and too many crossovers than to go after a female audience seriously. That's why any seeming attempts to appeal to a female audience turn out to be transparent at worst. In fact, it's also why not many women have been hired to write and draw for them: no doubt many women who'd like to get into working on their products would prefer to have the freedom to write self-contained storylines, and DC/Marvel's refusal to let go of crossovers only sabotages that. Just like plenty of male writers, you can be sure there's plenty of female writers who wouldn't find the idea of entering mainstream only to be forced into writing editorially mandated hack jobs very appealing.
And that's some of the reasons why they don't have a very big list of female readers and contributors, inside or outside, and so long as they remain that way, that's how it'll be.