Those who live in West Egg, like Gatsby, are also very wealthy, but they are the social newcomers who have made their money through commerce (legal or otherwise). They lack the sense of entitlement found among the East Eggers, and they are not "refined" or "polished" in their manners. Gatsby represents this social class. He owns a mansion and dresses well, but he lacks the background of an old and well established family. He is uneducated. He has a great deal of money, but he displays it very conspicuously--a sign of terrible taste to someone like Tom Buchanan.
By developing the social differences between East Egg and West Egg, Fitzgerald develops one the novel's themes. No matter how wealthy Gatsby might become, he would never belong to the Buchanan’s' upper social class because he was not born into it. He would always be an outsider.