Because those 300 million Americans shop at the same place, and, generally speaking, speak the same language. If I run a department store in England, advertisi

Because those 300 million Americans shop at the same place, and, generally speaking, speak the same language. If I run a department store in England, advertising in France doesn't do me much good. Ukranian universities don't much care about advertising in Spain. The US is the largest, richest single market in the world, with the possible exception of China/India. Those markets, however, are undeveloped.