In the Great Gatsby, money is one of the majors themes in the book. Not only how much money someone has, but how they went about getting that money. Fitzgerald makes it very clear that the wealth that Tom and Daisy has is superior to the wealth that Jay Gatsby has. Tom and Daisy were highly educated and came from money, while Gatsby got his money from selling illegal alcohol and throwing extravagant parties with the alcohol. He represents new money while Daisy and Tom represent old money.
The distinguishing between east and west egg is the best way that Fitzgerald describes the difference in wealth. Gatsby is forced to look across the water from his house in west egg while Tom and Daisy get to lavishly live in east egg. It is not that they are wealthier than Gatsby, it is just because of how they got their money, and the people that they know that allows them to live in east egg. I believe that Fitzgerald is using this as a metaphor to speak on American society at the time of the roaring twenties.
People in the twenties who were rich and had been rich forever represented the residents of east egg. I think he chose the east to represent old money because in America all of the people who came from old money would live in the east. All of the New England states, New York and Virginia were the original states that all of the wealthiest people came from in the early stages of American society. He refers to new money as west egg as a way to promote the new America that was formed by the frontier. People fled west in hopes of making it rich whether it be in the workplace, finding land, or striking gold during the gold rush. The west represents the new form of wealth, while the east represents old money. Honestly I can still see some of the comparisons of that today. The west is where all of the tech companies and new innovations occur, while the east is the home of Wall Street, and bankers who continue to try and make it big on a hundred year old profession.