I must admit, this thread has made me wonder, mostly about the topic at hand, but also about some of the other stuff.
Two events that struck me today made me wonder if it's an age thing? I attended a junior cycle event for all age categories up to 16. The split seemed to be around 50/50 between the sexes. I went to my BIL birthday bash tonight where someone had brought him the local rag from the old home town, and I noticed another friends twin girls were on the back page for athletics in the under 9 category. A year or two back, I was captain of the golf club, and as such was responsible for improving the flagging membership. We had lots of adult members, lots of juniors who played with their parents, but once they hit 16 we seemed to lose them, and we never really did pin down why.
I realise that my personal example includes the loss in equal measure to both sexes but I still wondered if it's a factor where returning cyclists is where the real difference becomes noticeable?