Gender differences in participation and reward on Stack Overflow
link.springer.com
link.springer.com
Furthermore, questions are a lot easier to ask imo than it is to answer a question, and the answer is the most important part since if a question helps more than one person many people have the chance and the want to ask it while to answer it someone would have to take the time to read the question and have the knowledge to be able to answer and the only reward is additional points on one's profile.
A good question should be more rewarded, but so many people don't upvote questions or don't even have an account or login anyways.