Remember what I said about milk going bad really quickly? That has been true for hundreds, maybe thousands of years. Historically, nature has dealt with the problem by storing the milk in the cow.
However, not all of us own a cow. Farming was invented so we would not have to. Farmers pull the milk out of cows so you can drink it. (Or they used to.)
Actually, in the United States, a lot of rural people still owned cows into the late 19th century. To provide milk to town and city people -- a population that grew rapidly starting around the time of the Industrial Revolution -- dairy farms, generally small ones, at this point, hand-milked cows and put the products into glass bottles, which were then delivered to customers.