This is pure speculation, but there also might be insurance money involved. I know players need to miss a certain number of games with an injury for insurance to pay their salary, and where JO had missed games previously with the wrist injury, they might be more likely to get some of his salary covered (I would assume if they buy a guy out, insurance is out the window).
Its also possible that they specially insured his wrist, since they knew it was an issue that would possibly cost him a large number of games.