I hate the bogus narrative that teams like the Packers and Steelers "travel well." They're wildly successful teams that have bandwagon fans all around the country. I can't tell you how many Packers fans I've met who have literally never stepped foot in Wisconsin.
Packers and Steelers fans typically attract the blue collar workers and traditional based fans due to how they were built. But their fans travel extremely well and they have a huge fan base. It's not even debatable Birmingham used to be called "little Pittsburgh" and the Packers were similar to Alabama in the 60's. So most Alabama (the state) pro fans started gravitating towards those franchises.
Cowboys are basically the Atlanta braves of the NFL because the exposure they got in the 70's through the 90's compared to all of the other teams. The emergence of Fox and CBS led to the even playing field, but they had already became America's team by then.
KC and Denver are all of the non Packers Midwest team. They have a significant following
49ers and Patriots fans mostly consist of bandwagoners. The Patriots fans now, will probably be like the 49ers fans now in that the 1st generation were bandwagoners and the next generation were born into it.
Then you have the "team" fanbases in which being a fan of that team means more than supporting the team. Examples are: The Who Dat nation, Browns fans, Raiders and Eagles fans.
You also have your player fans. Like Brady and Peyton followers. Similar to the Lebron fans who aren't Cleveland fans.
Finally you have your geographic fans.