Another view of why this happens:

"Whenever the subject of women in science comes up, there are people fiercely committed to the idea that sexism does not exist. They will point to everything and anything else to explain differences while becoming angry and condescending if you even suggest that discrimination could be a factor. But these people are wrong. This data shows they are wrong."

Lisa Shea, Low Carb and Video Games Editor
Low Carb Forum