Actually, I'm talking about the ones who say "no" when they actually do mean "yes" and get all weirded out when the guy disengages after she says "no." What the hell is the deal with that?
Dunno. Not being a female and all.
I would imagine for some that saying "yes" would imply that they are sluts, while saying "no" (all the time wanting it of course) would make it more like acquiescence than desire (which they don't want to admit they have).
My arm-chair psychologist view.