Participation is the key, if you look at the boys game you have millions playing it, clubs can pick up and discard huge numbers of boys a year, and simply keep the best ones. With girls its a hell of a smaller pool and you then have to work with the ability that you have. That obviously has a factor in quality.
Boys are lucky in some respect, as in all villages there will be several sports clubs (cricket, rugby, football) of which they are able to fit into, off the back of that they form friendships and social bonds with the players of their own age that are in the same systems as them. For girls there may only be one football/rugby/cricket club in their entire region, never mind their village, so instead of it being something simply there for them they have to go out and seek it.
As a father with daughters, i applaud the rise in womens Rugby/Football/Cricket, simply to offer girls the opportunity to play sport, which as a boy was a given when i was growing up.