In chapter 9, why does Nick feel that Gatsby’s tragedy is a contrast between East and West?

Although East Egg and West Egg populations look like they
are cut from the same cloth, there was a wide difference in their stature and
character.  East Egg was populated with traditional mansions and the people were from
"old money."  These people did not think highly of the "nouveaux" rich.  The "New money"
was sneered at and looked down on almost as much as the poor by the people of East Egg. 
West Egg was where the "new money" people lived.The people who had made their money,
like Gatsby, on gambling, illegal activities, or semi-legal activities were no match for
the "tradational old-money" people of East Egg, and considered vulguar.  The East Egg
were corrupt with their money and were out of touch with the real world because their
life was simply easier.

This is why Nick believed the
contrast between East Egg and West Egg can be drawn so clearly between Gatsby and Tom. 
Gatsby had all the money he could ever want, but he never understood the tight circle of
stature, tradation, honor among theives attitude of the Old Money of Tom Buchanan. 
Daisy could never leave someone like Tom, her type of man, for someone like Gatsby, a
man she was attracted to, but as a toy, not a
partner.

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"Those in the Midwest—the newly arrived Nick
Carraway—were fair, relatively innocent, unsophisticated, while those who lived in the
East for some time—Tom and Daisy Buchanan—were unfair, corrupt, and
materialistic."