I think the top ten hated is somehow a corrolary to the front-runner syndrome noted by my colleague, Dr. Fong.
There can't be any rationale other than a team with a long record of losing/mediocrity.
It's very probable if the team were to start winning, it would be less reviled. Regardless, it's not an appealing aspect of American culture, imo.
Addendum: I had not considered NoSaint's view that Buffalo is somehow equated with drunken louts. That's not my view, but I suppose it might be a popular image.