First, we must note that the world has not necessarily become more Americanized. We can argue that the opposite has happened. As the world has become more globalized, other countries have become more important. China has become much more important in places like Africa, perhaps becoming more influential than the US. Culturally, things like English soccer/football and Indian cricket leagues have become fixtures of the sporting world. This is not Americanization.
If we assume that globalization has made the world more Americanized, it is because American tastes have been accepted by more of the world. Globalization allows American movies to be distributed around the world. It allows there to be Disneylands in foreign countries. It allows people around the world to want the iPads and iPods that Apple invents. Because the US has been the world's largest consumer culture, its culture is the one that dominates as the world's consumer culture becomes more globalized.