Why are espresso-based drinks mixed with milk relatively unpopular in Europe, yet dominate here?
Tradition, mostly. Americans came late to espresso based coffees, and milk is plentiful and fresh in the US whereas it was often less so in Europe. ( I remember flying to Europe in the 70s with some German kids who marveled at how fresh and good tasting American milk was wherever one bought it, not so in Europe they said lack of refrigeration, especially in southern climes like Italy, was a possible reason). It seemed natural to add milk to us, and we had no traditions of decades duration which said not to add milk. Higher incidence of lactose intolerance on the part of southern Europeans has been suggested as a reason, but I doubt thats accurate.
