From Arizonas view, they wanted to add the cap hit from Datsyuk on 7,5 million to get to the cap floor. Its not the first time they done like this, they added Chris Prongers contract in the same way Before. Arizona have a very Young team which will develop and want bigger contracts in the future. Arizona will have room to give them bigger contracts.
Arizona also rated Jakob Chychrun who they picked with the 16th very highly. They overpaid quite much in my opinion but they have many prospects in their organisation so they probably see it as they can afford it.
Still a great trade from Ken Holland who is a master in this business.