Now that you've clarified what you meant, I agree. For 20 years the Falcons just seemed so clueless that it turned off the fans. The locals were used to football being played at a championship level in the high school and college ranks in the southeast so it was very distrubing to see a clueless and inept professional franchise.
Instead, the locals preferred to follow the Cowboys, Steelers, Dolphins and Raiders.
This is true of almost any team though. The Patriots fans are everywhere now, but where were they in they late 80s to mid 90s?
The Bears games in Chicago are a tradition but professional football in Chicago has been played a lot longer than in many other cities. The Bears also have a rich history - many younger teams like the Falcons just don't have a rich history to build on.
Some of it's history, some of it's just general team loyalty. I never heard the Pats having a hard time getting butts in the chair, but New England (Boston really) sports fans are long suffering, they're used to supporting bad teams with no chance of a championship. And a lot of it is the area, Chicago is a general sports town, as long as management doesn't completely screw up anybody there can sell out. Denver is an NFL football town, the Broncos will always sell out. The south east runs strong in football, but not NFL football, that makes for fair weather fans. Arizona has no true sports tradition, we're totally fair weather fans for anything at any level.