To answer your question. Why we don't drink milk? Simple. The dairy industry puts cows through literal hell during their lifetimes. They are treated like commodities from the moment they enter this world. The dairy industry's cows have the same fate as the meat industry's cows. When their milk production drops, they are slaughtered. No cow is permitted to live out their normal 25-year lifespan. In truth, the dairy sector exploits cows, and 20% of the beef sold in shops comes from them.
Calves will spend most of their life in cruel confinement after being taken away from their moms. In fact, most will spend their first two to three months of existence confined in barren hutches, fed a diet of milk replacer while people sip the milk meant for them.
Over 90% of dairy cows in the United States are confined to mostly indoor operations, with more than 60% chained by the neck within barren cubicles, unable to conduct even the most basic activities necessary for their well-being. They are then forced into stun boxes They are shot in the head inside these chambers in order to render them unconscious. In fact, when their throats are sliced, many are still conscious.

To challenge your claim, I will just put here a harvard's report's excerpt.

—When it comes to overall health benefits, it seems that dairy is neither a hero nor a villain. Adding some dairy to your daily diet — a splash of milk in your coffee or a cup poured over your breakfast cereal, or a slice of cheese on a sandwich — can help you get some of the vital nutrients you need. “But keep in mind that eating a well-balanced diet that includes plenty of green leafy vegetables and nuts can better help you get the calcium and protein you need rather than relying too much on dairy,” says Vasanti Malik, nutrition research scientist with the Harvard T.H. Chan School of Public Health. (By Matthew Solan, Executive Editor, Harvard Men's Health Watch)