I'm coming late to the party...
As my kids were growing up. I often looked at the whole sports thing and how many men (boys) participate in a given sport vs. how many women (girls). Men usually outnumber the women. When I looked at which gender created the sport, most have been created by men. So it made perfect sense more men would participate.
When I was growing up there were no sport teams for girls. That alone will take a lot of girls/women out of the ranks of participation. Today that's no longer true so more girls are getting involved in sports at an early age. And they often stay involved.
Even though doors have been opening up for girls in the sports arena, there still exists gender roles that parents, family, friends, teachers (consciously or sub-consciously) steer the children towards, depending on what's between their legs at birth. And if parents are honest, many will admit they have dreams of their kids growing up to fulfill society's image of the perfect man and the perfect woman. We humans do like conformity. It makes things easier for us, but not always for the child.
I doubt women will ever equal the numbers in sports as men. But if we just stopped putting people in a box based on what we see, there will be less obstacles for those who want to participate in activities society doesn't deem "normal" for them.
But what is "normal" anyway? That's easy. Since no two people are exactly alike, normal is unique.