[giulianob]

Actually we haven't evolved to digest milk after childhood that well:

    While most infants can digest lactose, many people begin to develop lactose malabsorption—a reduced ability to digest lactose—after infancy. Experts estimate that about 68 percent of the world’s population has lactose malabsorption.1
    Lactose malabsorption is more common in some parts of the world than in others. In Africa and Asia, most people have lactose malabsorption. In some regions, such as northern Europe, many people carry a gene that allows them to digest lactose after infancy, and lactose malabsorption is less common.1,2 In the United States, about 36 percent of people have lactose malabsorption.1
    While lactose malabsorption causes lactose intolerance, not all people with lactose malabsorption have lactose intolerance.

https://www.niddk.nih.gov/health-information/digestive-disea...

[googlryas]

Maybe "we" as in humanity haven't, but "we" as in white people from Northern Europe have. Even in the most lactose-malabsorptive place (Middle East), 3 out of 10 people can digest lactose successfully.