In fact, we do not know the full reason behind this, but the incoming texts are the ruling.
It is not possible to make two leaders in the family, each of them using his right, that makes the children lost.
On the other hand, upbringing is shared between the parents, and is not specific to the mother. As for childbirth, it cannot be made a reason to make guardianship for her, as is clear, since a man cannot conceive and give birth, except that he is legally responsible for managing the affairs of the house, while none of this is obligatory for women.