The Seahawks couldn't have kept Hutchinson even if he wanted to. There was a clause in the contract given to him by the Vikes where he had to be the highest paid offensive lineman on the team or it would trigger a sh!tload of money that had to be paid to him. Walter Jones was higher paid than the contract Hutchinson got and the Seahawks could not handle the cap hit which would be triggered by that clause. Their hands were tied.
They didn't not keep Hutchinson so they could get Burleson. It was more of a revenge factor, but it was stupid anyway.