I'm guessing Marvel, DC et al have done a lot of research over the years and found out yep, it's pretty much only males that read comic books. They've attempted female-targeted comic books over the years and they don't sell. Not really worth spinning your wheels on something that's not going to happen.
> A book store will have many types of books including romance novels, but comic book stores may have just one type of comic, and it's usually for men.
Men and women shop at book stores, so there's that. Comic book stores (are there more than a couple hundred left in the US anyway? Who cares) are really only frequented by men because WOMEN DON'T CARE ABOUT COMICS. No amount of hand-wringing over this issue is going to change it. Sometimes it really just is "men do this, women do that". It doesn't need to be over-analyzed.