Fans tend to take a sense of ownership over their team, and that extends to key players. There are just some players who would look completely absurd ever wearing the uniform of another team. Just look at Tom Brady wearing a Tampa Bay Buccaneers uniform. It just looks unnatural. He’s a Patriot.
So were players like Hines Ward, Troy Polamalu, and Heath Miller Pittsburgh Steelers. Not every great, even in Pittsburgh, finishes their career here, of course: see Alan Faneca, James Harrison, Rod Woodson, for some of the more prominent examples of somewhat more recent vintage. Antonio Brown and Le’Veon Bell just joined that club.