Why does the cow only give buttermilk?

Cows produce buttermilk as a byproduct of the butter-making process, not as a primary product. When cream is churned to make butter, the liquid that remains is buttermilk. This nutritious liquid contains some fat, proteins, and lactose, but it’s distinct from the milk the cow produces, which is primarily whole milk. Thus, buttermilk is a result of processing milk rather than a direct output from the cow.