I have no clue. But I think in general, perhaps it is a societal as a whole thing. In the UK I feel much more at home for many reasons, and I think it is because I don't notice the weird looks and derogatory views of women. Not that the caving community here is bad, I just mean society as a whole in the states is much more backwards than you'd think. All this religious shit isn't doing us any favours. I mean you do know they are trying to take away our rights to birth control and such again, yes? Old world extreme religious views permeate society here, so I think it's just a trickledown effect perhaps. I find the UK much more progressive. Also, here caving isn't very widely accepted, we dont have uni clubs and things like that, so we aren't getting to the younger and more empowered generations where women /would/ want to cave.
I mean, that being said, our grotto (cave club) executive board is probably one of the best ratiowise in the nation, haha. Myself and four others are female ^.^ so exactly half our e-board! The particular grotto I am in has some decently active females, much better than the typical norms or national averages.
For vertical stuff though, still, severe lack of skilled females. I"m the only one I know in this area with the experience and training to do long rope, for example. At our team practices there is sometimes one to three other females...one from Alaska, one from Indiana, and one from Virginia. there is another in North Carolina I think. Offhand though, so that's five total females i know of in the entire united states who are well trained for long rope. Ignoring population size differences, that would be like the equivalent of five females in the UK qualified to do your deep push expeditions in Europe. CRAZY!!!! I mean there are quite likely those I don't know who are in the US who do such things - the US is huge after all - but the point stands...if that's as few as I know and I'm on the team that holds world long rope records....clearly they are not common.