Because within  U.S.A. cultural outputs there is nothing intrinsically American that hinders our understanding , therefore allowing its easy consumption. Let’s use an analogy:

Let’s pretend culture and its outlets is a ship. This ship is anchored to the bottom of the sea by links that make up the chain; that is, rooted to its country and people through a series of innate factors -such as language, folk references, etc. As long as we do not possess that anchor we will not be able to pull the vessel towards us. Basically, as long ad we do not  [try to] understand the vernacular means we will not be able to consume that culture. No body likes what they don’t fully grasp.

American culture, on the other hand, is a boat floating  merely over the surface, with no specific attachments [in fact, one could argue that the U.S.A. found its culture through exporting it both internally and abroad, a remarkable and loable task]. It is easy to pull and take it; even to appropriate.

Because U.S.A. cultural outlets lack something intrinsically American, it is easy to understand and, therefore, easy to consume.