Centuries of evolutionary biology and social conditioning has led men and women to have very different preferences when it comes to risk bearing and physical activity. Its not surprising that cycling is disproportionately male since it is both perceived as risky (for good reasons) and physically exertive. I understand that this is a cycling forum but if you take a step back and examine all the risky physical activities that we encounter in our daily lives (e.g. fixing a leaking roof) its not surprising that men are often called upon to fix the situation because we are conditioned (both evolutionary and socially) to be less risk averse than women. It all begins when our 4 year old son falls off his bike and we tell him to stop crying and get back on, but when our four year old daughter falls off we rush to cuddle her and tell her she doesn't have to try again until she's ready.

This isn't an endorsement of heteronormativity or gender roles but a simple explanation of why bike commuters tend to be predominately male. You'll also see this trend in any profession that includes physical activity and a large degree of personal risk taking (e.g. police, fire marshals, construction site workers, etc).