I think the biggest factor in the Cubs decision was regression from some of the younger players they expect to be the corps of their rebuilding. I'm speaking specifically of Rizzo, Barney and of course Castro who was signed to a large contract.
They will go nowhere without building a starting rotation that can go farther than six innings. I like Wood and he seems like a nice piece to build around. Samardzija has flashes of dominance but suffers from the same emotional failings that Gio Gonzalez suffers from at times. When things don't go well he seems to get down and let things snowball.
I hope they can secure a manager like Girardi because I think we can all agree that the Cubs being competitive is really good for baseball.