Sherman is the smartest of the 3, and I think he may understand his image moving forward, his ability to land big time endorsement deals is highly dependent on being with a strong defense that allows him to shine. I absolutely love Sherm, but if he were to go to a team without Thomas/Chancellor would he really be the same player? Would he take the same risks he does now to make a big play without an amazing defense to coexist in? How much better is Sherm on the field because of Thomas and the rest of the defense?
He's an absolute star now in the NFL in his 3rd year in the league. How many defensive players have EVER become as household of a name as Sherman has that early in their career? He's one of the most marketable players in the league at the moment and that will continue as long as he is with a core defense that allows him to shine. This, may account for more money overall in Sherms pocket than a couple million per season elsewhere, which is why he may be more reasonable with a contract than trying to max out the Hawks budget.