Apparently because in the womb and whatever, The X chromosome is the default and before the Y chromosome kicks in, the fetus develops as a female, (or maybe its better to say default state???) and shit.
Then the Y chromo gets its shit together, but not before those lil' nips come in.
And if the Y chromosome doesn't get its shit together and the fetus survives, you get an androgynous-strong baby that's a girl, genital wise. And also infertile.
Yeah this guy is pretty much right I think. In the womb and whatever, I think it's argued whether or not it develops as "female" first or if it's like you said just some sort of weird limbo default land.