How is The Great Gatsby a story of the west if it happened in the east?

None of the principal characters is originally from the East. Nick is from the Middle West, although he never mentions the city. It may be that it is St. Paul, which is where Fitzgerald was from. Gatsby is from South Dakota-although oddly, when Nick asks him what part of the Midwest he is from he says, "San Francisco." Tom Buchanan is from Chicago. Daisy and Jordan are from Louisville, which while not in the Midwest, is a very different world from that of New York. So they are all transplants, all hoping to create different types of lives for themselves in New York than they could have had if they never left home.