Although we can definitely choose from a lot more kinds of milk and its alternatives than our grandparents had growing up, cows remain a dominant enough source for our milk that we'll assume that's what people mean when they say "milk" on its own.
However, that's not necessarily true everywhere in the world and it never really was. Because while you might have heard of some parts of the world where goat's milk is a more common choice, it's also true that camel milk is considered an important staple in parts of Africa and the Middle East.
However, there's one key reason why international markets are starting to open for camel milk and several more as to why the steep prices customers pay for the stuff aren't likely to go down.