Breast milk evolves with the baby. The fat and other nutrient concentration changes as the baby gets older. Also, if the baby is sick, the breast milk will contain antibodies to help fight off the disease.

We don’t really know how the mother’s body senses these changes and adapts the milk. And we don’t have a good way to store antibodies in formula on a shelf somewhere for several months.

We could probably get pretty close by further breaking down formula into stages: 0-3 month milk, 3-6 month milk, etc. But that adds a lot of complexity for very little improvement in quality.