I'd like to add my two cents to the discussion.
In roleplaying many of us are familiar with the expression "Mary Sue". We all seem to agree it's about a character who is too perfect and flawless, or too powerful so they can't be challenged by anything that happens in the story, or someone who everyone likes.
Ever since the term became something we all use, people are terrified of doing things that would lead their character to be called a Mary Sue. Now, interestingly enough, despite the fact that both males and females can be Mary Sues, we tend to react faster to females showing signs of being Mary Sues than we do with male characters. And this isn't out of malice or sexism. The thing is that since the term was created based on female characters who displayed these kinds of traits, we tend to relate them a bit more with female characters.
What does this mean? That sometimes roleplayers won't be willing to do certain things they'd do with a male character if their character is female, mostly because they don't want their character to be labelled as a Mary Sue.
To think of a common example, think of a character like Superman. He comes from another planet, is incredibly powerful to the point where most weapons are useless against him, and one of the only things that can stop him is kryptonite. Besides that he's pretty unstoppable. If you created a female superhero who comes from another planet, has all sorts of superpowers and is almost unstoppable, except for a single weakness, I'd bet that a large majority of readers will start getting Mary Sue vibes from your character. And it's not because Superman is a Mary Sue, far from it. What I mean to say is that people tend to label female characters as Mary Sues much quicker than they label male characters as Mary Sues.
In reality, I'd say the definition of a Mary Sue would be someone who distorts the story to center around them. It doesn't have to do with an overpowered character or a perfect character, though those are common traits in a Mary Sue. A Mary Sue will distort the story and become the center of the universe. Everything must lead back to the Mary Sue. Everyone who is good will like her, and everyone who is bad will hate her. Everyone who is right will agree with her, and everyone who disagrees with her is wrong or evil. A Mary Sue doesn't allow for a proper plot to form, because the essence of a Mary Sue is to be the center of the world it lives in, and everything else merely exists to show how special, good or unique the Mary Sue is.
I'm aware that this is just a hypothetical possibility, and that many roleplayers probably have different reasons for why they won't play a strong female character, but this is something I encountered a few times. It has to do with our perception of the term "Mary Sue".
That being said I actually love roleplays where a female character plays a more dominant role. I had this roleplay once where my roleplay partner had a female character who was a skilled scientist, and she had brought together a team of superheroes. She was basically the leader figure for the team, and the one that kept them all working together. She hired an assistant (my character), who grew to develop a crush on her, and his job was mostly to help out with anything she needed, and he had his own robot helper as well.
While the superheroes were doing the actual fighting against villains, it was the scientist who was the true leader of the team and the one that everyone respected and followed. It really made for an interesting dynamic that I don't think I've seen in other roleplays I've been in. The superheroes themselves were young adults, but they didn't like each other, they would bicker with each other and the scientist had to try and get them to get along and work together. At times she seemed like the mom for the whole team. And of course, I had the lab assistant who was basically there to help her, and had a huge crush on the scientist, though so far the RP hasn't really gone anywhere with the potential romance plot, but due to the nature of the RP, I'm sure the scientist will keep her dominant role even after she and the assistant become a couple.
So... yeah.
