There is a logistic requirement to consume milk.
The dairy industry produces food, clothing. lubricants, glue, drugs, and vaccines the list goes on and on.
Add to this the value of farmland, the distribution network the value of investments tied up in one way or another, the fact that many farms are mixed and other products from them would not be as economically viable, likely costing more to the consumer.
Milk was seen as being necessary to make up for deficient diets in much of the industrial world even though it was proven later on to be a source of many infections. Despite the latter our ancestors still thought it was well worth the risk, such were the benefits conferred upon milk drinkers.
I don’t condemn vegetarians but they do seem to have this mission to make the world feel guilty.
Vegetarians do not seem to have any sense of scale, or at least the most fervent ones, the meat and livestock industry is a vitally important resource and if there are ways we can supplement our diet without products derived from theat industry there are still all the other non-edible products to account for.
There are also the effects upon the environment, we have been livestock farming for so long that many species directly benefit from the environment that we have created, many farms in the UK have not felt the plough on their land since Saxon times and even beyond to the Romans. To give up livestock farming would mean to change exclusively to crop farming.
The loss of such habitats would undoubtedly endanger many species.
Crop farming, which is the vegetarian utopia, is not free of environmental problems either, what with the natural production of organic run-off from the land into water courses.
Milk is an essential part of the livestock industry since it is so intimately involved in calf production, if you stop drinking milk altogether then like a row of dominoes other parts of the farming industry become uneconomic and the cost will always end up passed on to Joe Public one way or another.