It’s American because science fiction is about pushing back boundaries and borders, and that has been an American thing lately. In many ways, science fiction is the heir of the classic western, but there’s more to it than that. SF is a genre that can encompass any other genre and is one of the few mediums where you can have a novel that is A. genuinely entertaining and B. genuinely about Something. “Literary” books tend to be dull, and “exciting” books tend to be stupid, but in SF, you get both.
The whole idea that literature can only be about normal folks living normal lives amongst crushing normalness is very, very new. Literature used to almost always be about the fantastic. I think Gene Wolfe (a Catholic sci-fi/fantasy author who uses Catholic imagery in his writing) has an essay about this, and why the folks who teach that real “literature” can only be mundane are just a recent and sickening abberation.
Freegards