I always hated how Miami stadium were half full if something wasnt on the line, but I actually herd Colin Cowherd give a good explanation that spans not only across the NFL, but into other sports as well.
Buffalo is a small market. That's not a bad thing, but it's a fact. Miami is not. On a Sunday afternoon in Miami, there are other places to be. The beach, malls (which arent so much about shopping as they are about socializing), boating, fishing, restaurants, other sports even. Same in San Diego, LA, Tampa. Because there's so much competition of things to do, those fans that arent die-hard go do other things. Mid Decemeber in Buffalo, football is life. Not so much in Miami.
I wish we had more die-hards, but sometimes if the choice is Bikini clad women and a frosty beverage in my hand, that's hard to pass up.