Questions on the Great Gatsby

Well my questions are quite general, seeing as their were so many characters introduced. The title seems misleading as this story is not only centered in the form of Fitzgerald, but also Gatsby, why did the author create more unnecessary characters? Though other stories such as "Tuesdays With Morrie" seems to center in the honor of a person, but the format is much different than this story. The story overall, was interesting, but I could not help but to compare it to Tuesday's with Morrie. My judgment rates Tuesday's with Morrie much higher than The Great Gatsby.