Many cows are given hormones so that they will produce milk even though they don't have a calf to feed. That is considered unatural and against what vegans believe.
Why are vegans so against milking cows? OK I live in the country by many diary farms, I've seen cows get milked they're not harmed in any way and they are healthy as ever and it does not harm the calves.
I'm not sure, vegan are weird. Like cross-fitters.
Some cows do not live in very pleasant conditions. They are treated cruelly, and the milking is painful for them. That is why. Honestly, I think that if you know that the company treats their cows properly, it's all right for vegans to drink/ use cow milk.
Apparently there are some dairy "factories" that just line up the cows and milk by machine, and I forgot what I read but they either inseminate the cow over and over or they make the cow take hormones to make her continuously produce milk. Then they kill off the calves because there are too many.