Fathers are different from mothers.
Babies learn that very early.
Fathers have fuzzy chests, deep voices, big hands, flat shoulders. Mothers are softer and smell of the milk that soothes away hunger and fretfulness. Those are quiet, needy sounds. Fathers are different from mothers, and no father in the history of the world has ever breastfed. For a father to mimic female biology, either Mom has to express milk and someone has to wash the pump, store the milk, fix the bottle, wash the bottle, and put everything away, or the baby has to drink a commercial substitute that causes internal changes.