I would imagine that fewer commuting women also has a lot to do with the fact that there are more men in the workforce than women. Plus, for the women that ARE in the workforce, there are risks/issues to commuting to work that a lot of women don't want to deal with: helmet hair, carrying/changing into non-cycling work clothes, the risks of riding alone...

For group rides, probably has a lot to do with women being moms. I know when I was a SAHM, I never had the chance to do group rides because i so rarely had any kind of alignment between my childcare schedule and group ride schedules.