Why Did F. Scott Fitzgerald Write About the Corruption of the American Dream?

          F. Scott Fitzgerald wrote book "The Great Gatsby" during the 1920s, a time that was characterised by wealth and art and fun. It is also known for the American Dream: each person is able to make as much money as inherently possible, and they can end up in any social class regardless of their birth or family.
          I think that the primary theme of "The Great Gatsby" is the corruption of the American Dream. My question is, Why would Fitzgerald write about this during this time where America was flourishing, and he himself was considered by many to have achieved or be very close to achieving the American Dream? At this point in his life, he seemed to have it all. He had one over and married Zelda, and he was very rich because of his writing. So why did he write about the corruption of the American Dream?
          I think that he seemed like he had it all together to a lot of people, but when he was in France trying to write this book, he didn't really. He had a lot of money, but his relationship with Zelda was failing, and he was a raging alchoholic. I think he was writing his failures into his book.