If they aren't willing to go watch a bad football team play in bad weather they aren't serious, at least not about that level of football. As you point out the south east really ruled by college and even high school football, that kind of makes them fair weather fans when it comes to the NFL. Can't say as I blame them there's a lot of good college and high school football played down there, no reason to pay more for worse. But within the NFL compare them to the NFC North (formerly NFC Central), teams that have had long stretches of serious sucking and not much difficulty getting butts in the seats regardless of the weather. I think for some of those years there was a large body of fans who took pride in being demonstrably tougher and more dedicated to football than their team.
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.