Oh the bovinity
There's some OK analysis further in, though I think they overlook the impact of demographic changes, lactose intolerance, and some other factors. The main problem for US milk providers is that most milk sold in the US is not very good. Farmers like Holstein cows which give maximum yield but the milk is not very creamy. If you can get milk from Jersey cows it's like night and day - big gobs of cream floating in it, and you can appreciate how milk functions as food. Don't get me started on 2% milk, which should simply not exist.
As so often, profits are shrinking because an industry got greedy and took up the pursuit of the lowest common denominator instead of the highest common factor. See also: journalism.