It wasn’t a matter of what God the Father did for Mary, but what he did for Jesus. What so many people don’t understand is that the Immaculate Conception of Mary is all about Jesus. It was because he was to take on his human nature in her womb that God deigned her to be free of all sin and therefore “full of grace” (Lk 1:28). It would be unthinkable, given the revelation that we have in Scripture and Tradition, for him to be conceived in anything but a holy place. David, Abraham, and Moses weren’t called to give birth to Jesus.