Second, your words sound pretty crass about "the Ark delivered the goods." Mary was not just, in a physical sense, a "reproductive unit," a procreative utility to be picked up, used, and dropped, a kind of rented womb. She was the Daughter of the Covenant, Bride of the Spirit, Mother of the King. She personified Covenanted Israel bringing forth the Messiah, and with a personal, intimate, and permanent covenant relationship with the Him. Even before she conceived Him, she was Kecharitomene, an incomparable vessel of blessing.
As Jesus said --- rejecting mere biological reductionism--- "Don't just say 'Blessed is the womb that bore you, and the breasts that nursed you." Rather, "Blessed they who hear the word of God, and kept it." Mary, par excellence, heard the Word of God and kept it.
Do you think God would have thrown this Covenant Daughter, this Bride of the Spirit, this Queen Mother, back to Joseph, like "Here, I got what I wanted, now you can have her"?
Impossible. Unthinkable.