The ending to Fitzgerald's work brings to light several elements that help to solidify the work as an essential component in the understanding of American History of the 20th century. The ending where there is little resolved in terms of moral absolutism is a powerful one. Those guilty do not receive their justified punishment and those who are innocent are not going to receive full absolution. Nick repudiates the lifestyle of Jordan, Tom, and Daisy, but this does not stop the wrongs perpetrated to continue. Part of the reason why this ending works is that it represents a great deal of American History. Whether or not Fitzgerald intended, his conclusion where moral judgments are not fully recognized in society as one where virtue is rewarded and vice punished. In some respects, the ending "works" because it has been proven throughout American History, a narrative where good individuals and bad ones have not often received the fairest of decisions. From a larger standpoint, this ending works because it reflects the tragic condition in which human beings find themselves. There is little in the way of alleviation of such a predicament. In the face of such an element, human beings have little else but to "beat on" as "boats against the current."
The novel ends the way it does because there really is no other way for it to end. As a modern tale, The Great Gatsby is a reversal of the way stories were told in the 19th century. In the typical "old fashioned" story, the good guy wins (and gets the girl) and the bad guy loses. In modern storytelling, the bad guy wins (and gets the girl) and the good guy (in this case, Gatsby) loses. In fact, all of the characters in the novel who represent innocence, human potential, or are caught in the power struggles of others (Gatsby and the Wilsons, namely) are the ones who end up dead. They are the dreamers. The vile characters (Tom and Daisy) get off scot free. Nick is detached enough to recognize the tragic elements of Gatsby and the Wilsons and the shallowness and hollowness of people like the Bucannans. This is why he spends the last page of the novel reflecting upon these events on the shore watching boats go by and pondering what the old Dutch sailors must have seen when the first beheld Manhattan and Long Island in the 1600's. Fitzgerald suggests that in the modern world, the dreamers, who hold on to the ideals of America's romantic, agrarian past cannot survive. Those who embrace the ideals of the modern world--industrialization and modernization--thrive.