Like it or not—and most do—team pride is a huge part of the game, even in the era of free agency. There are still a lot of players who strongly identify with their organization and the culture that they build, and this is especially true for flagship franchises such as the Pittsburgh Steelers and the Dallas Cowboys.
For Dallas, the Cowboys star is the closest thing that you get to sacred in the game, and when Terrell Owens many years ago ran up to midfield after scoring and celebrated on it, that caused quite a kerfuffle, to say the least.