I think it's more a fact of describing the life of upper class people. The poor characters are not so well painted too. But they live (or want to live) in the u

I think it's more a fact of describing the life of upper class people. The poor characters are not so well painted too. But they live (or want to live) in the upper class world, in the book. We have only flash of the world of the "poor". The narrator, also, is from a bourgeois family (Nick graduated from Yale). So maybe it was just a novel describing a world. A World fading away.