All you have to do is look at what the League did through all the realignment efforts. Look at how there were many moves to place teams in a more geographic setup. Now look at the NFCE. Everyone with the exception of the Cowboys is an East Coast team. The reason Dallas remained there was the old time ancient and fierce rivalries with all of those scumbags.
.. that time when Harvey Martin threw a black funeral wreath into the Skins locker room during halftime of a Thanksgiving day game ..
Also someone let some white chickens loose at RFK Stadium, as well. It may have been Tex Schramm. Need to look it up. I can't recall the reasoning.
Then Clint Murchinson purchased the rights to "Hail to the Red skins" song in 1960. As the owner was strongly opposed to Dallas getting an NFL team.
So he purchased the rights to that song, so they could not play it at their games anymore. So they made a trade, song rights for the yes vote.
How about Whistlin' Ray vs. Washington Indian mascot, can't remember his name, they always had fun on the sidelines and end zones.
Then the tom Landry American Express commercial. It is on YouTube.
That was some great stuff that fueled the rivalry.