drafts are a last-resort policy. they're there as a big red panic button and the reason they aren't going away is because there's an incredibly, immensely small chance that, maybe, we'll need one in the future. as it stands, our military is probably more than sufficient for any current wars we might want to fight. the future is uncertain, voluntary military participation may, at some point, drop to levels low enough that we are unable to fight a war effectively, in which case a draft would be necessary for our own survival as a nation. but nobody wants to be the one to press that button, because it's basically asking for people to stop trusting your government.
the inclusion of women in the draft is an acknowledgement of the fact that women are now allowed to hold combat positions in the military. if women are eligible to participate voluntarily on the basis of equality, then it is reasonable that they should also be candidates for involuntary service just as well as men. the fact is, of course, that the draft is bad for everyone, and everyone knows it.