First of all, I'm not an american, so I don't know all there is to know about your political system. I know very few vote, and that's a problem of course, but it can hardly explain the lack of women (which was originally about Belgium, if I'm not mistaken).
I can't explain, that's the problem, and I don't think you can either. Politics is all about fixing things that won't run smoothly without intervention, don't you agree? I don't think the 'universal' right to vote has much to do with how the office is set up, since most people doesn't vote on individuals. You accept the list that has been made by the party, since it would be a fulltime job to investigate every last one of them. Politics is also a lot about bargains, and I do think women somehow are being excluded here. Men are default, and a woman is only chosen if there's any gain, if you know what I mean.
I'm not sure a "ratio-rule" is the way to go, and it's clearly hard to enforce, but what to do? If I would assume women aren't less into politics, aren't uneducated and has the ability to think abstractly, what's keeping them out? What can be made to get them in? I do not know. *I* just think it's a shame (that should have gone away a long time ago), and we can't consider women equal if most of the people in power are men.