A lot of it deals with the stigma.
People will tend to take women less seriously if they give an idea than a man if they give the same idea.
To put this into more detail. If a woman came up with an idea for a comic book movie, and was scoffed off about it, a man could say that exact same thing and be lauded for it.
Unfortunately, geek culture plays into sexism since the industry is not as gender friendly as other businesses. Part of this has to do with the industry being considerably younger than, say, being a scientist. Another part of it is because the Internet plays a large role and some of the worse parts of human thought come out from the ugly shadows of things like Youtube comments, or Facebook replies.
I mentioned scientists earlier as a comparison, but that industry hasn't been the most friendly either, as evolution is that industry comes over time, as well as gender equality. One of the most noteworthy instances comes from Rosalind Franklin, where her work in X-Ray Crystallography is largely under-credited and the discovery of DNA (which is huge for genetics and biology and biochemistry in general) gets largely credited to Wattson and Crick, the former of which is well known to be a racist prick, and he even went so far as to say that blacks have inferior genes to white people.
The last note, and the most dire one, is that women are much more likely to be sexually harassed then men. Sexual harassment to men can happen, and that should be frowned upon as well, but women face this more often, and more on a timely basis to men. This is extremely important to note, because equal opportunities means an equal environment. Even if a woman got equal pay as a man for doing the same amount of work at the same job, there is no true equality if a woman has to endure ridicule and harassment.