Speaking purely cinematically, we can say that film, like literature, deals often in tropes, types, and recogized personas. The stereotypical/archetypical American film figure is sometimes seen as the "gun-toting hero".
This vision of the American, in film, mind you, is especially visible in foreign films of the 70s, 80s and 90s.
So, maybe the reason that the hero is American has something to do with cinematic type and tradition as well as the other, more general cultural forces mentioned above.
While there are many, many excellent British films, some are heartily received in the States, but others are not as popular, simply because tastes differ in different cultures. Likewise, other European countries' films are less accepted than the British simply because the commonality of language affects the reception. Certainly, the types of humor also determine the reception of a film. Even in America, satire and sarcasm are much more heartily enjoyed in the Northern states over other geographical areas of the U.S. Simply put, there is no denying that culture affects cinematography.
I must agree with littleteacher in saying that Americans are simply self-centered when it comes to movies (and many other things). For example, I cannot think of a foreign film festival as big as Cannes in America. We, Americans, tend to like our "own stuff."
Well, it is natural that Hollywood, as an American film industry, is going to root for the American, and frown upon films or stories where Americans are shown to be "losers" or to not be the heroes of the film. This is just pure nationalism, which of course every country is subject to. The fact that America is one of the world leaders in film-making means that they subject the rest of the world to such stereotypes as the American hero.
I think we Canadians like the Americans completely...
But movies like "redacted"...act
lost and failed in America.