Sherman and Pete Carroll don't get along. Sherman has publicly criticized Carroll. Seattle is desperate for o line help and Lindsey is young and an above average if not borderline pro bowl center. Seattle also needs more weapons and Cobb is also still young. He showed in the NY game that he can still be a dangerous slot receiver. Another reason is this years draft is deep in cb's. Seattle could spend their first round pick on a cb.
Well they seem to be succeeding just fine regardless of any differences they're supposed to have.
The Hawks' OL is horrible, but center is the one spot where they're set. Britt bombed at tackle and guard, but he's found a home as a good center. If they made a move for help up front, it won't be at the pivot.
With Baldwin, Lockett, Richardson, and Kearse in house they really don't need receiver help. And they certainly don't need someone in the style of Cobb. And lastly, who is going to look at what Cobb is doing with Rodgers and think he'd be a good player to trade for?