Uh, the reason we don’t drink human milk is simple thermodynamics. If adult humans drank human milk, the milk providers would have to consume more calories to produce the milk than the milk itself would contain.
Cows can eat grass and other substances that humans cannot. The cows eat the grass, the cows make milk, we eat the milk.
Now, what about the healthiness of human milk vs cows milk? Well, every mammal has a different milk composition, depending on their lifestyle. Animals that spend a lot of type away from their young have concentrated milk. Animals that spend a lot of time with their young have dilute milk. Some have more sugars, some have more proteins, some have more fats. Whale milk for instance is almost 50% fat…much richer than heavy cream. Cow’s milk has much more protein and fat than human milk. Human babies fed cows milk will often have allergic reactions to all the protein in cow’s milk. Human milk is low in protein, low in fat, but high in sugar and water.
But human milk isn’t neccesarily going to be better for an adult human than cow’s milk or goat’s milk or rat’s milk. Human milk is perfect for human babies, but adults have different needs than human babies do. Adult humans do not need any dairy products in their diet, and many adult humans have difficulty digesting dairy products. So cut out dairy altogether. Or not. I personally enjoy dairy products, even if they aren’t neccesary or even healthy. Chocolate, beer, and lard aren’t neccesary or healthy either, but they are delicious.