quote from this article. Milk Campaign Hits 200th Moustache

Milk is not a sexy drink. Despite its fun, Freudian calling-card (the milk moustache), moo juice simply doesn't have the social cachet of coffee or bottled water.
Maybe it's a matter of bad public relations. Maybe it's because milk strives for immortality by turning into cheese after a few months in the fridge. Or maybe it's simply because milk is a maternal lactating secretion, something that's hardly, um, titillating.