Why do the Dallas Cowboys play in the NFC East, if they are in the southwest?

To keep the tradition of the same great rivalries with the giants, eagles and skins. The division name is just a name of the particular division, not necessarily a geographic locator. If that were the case, many changes beside this would be made. Teams such as the Dolphins should very well be in the AFC south, moreso than the Colts, but traditional rivalries with the Bills, Jets and Pats keep them in the East.