From Ask MetaFilter: Why is there no more milk delivery in the US? It used to be common, now it's extremely rare. Why is that? The short(ish) answer: First, larger dairies meant cheaper milk, making it harder for milkmen to make a living, especially since they had to wash and reuse the glass bottles. Second, the advent of both supermarkets and cars meant housewives could buy supplies on their own schedules. Perfectly valid reasons, but man, plastic jugs and cartons are so dull.
(Ronnybrook Dairy's milk is fatty and delicious, but I will cop to buying it at least partly because it comes in glass bottles.)