Deans has selected his players based on his game plan. Would you play McCabe at 12 if your plan was to go from side to side in three passes? No way in hell.
The plan is obviously to have a backline full of players who are positioned well in defence and tackle well:
Genia, O'Connor, Cummins, Ioane, Tomane, Lealiifano, Horne, AAC (Adam Ashley-Cooper), Barnes - Check
Have a forward pack that performs around the park, pick-and-drives well and wins their set piece:
Robinson, Moore, Fainga'a, Alexander, Slipper, Horwill, Simmons, Douglas, Mowen, Gill, Hooper, Palu - Check
Have a halves pairing that runs very well in tight spaces and can easily turn a 5m burst into a 30m run:
Genia, Phipps, O'Connor - Check
And a backline that can take the highball well:
See all backs selected - Check
Cooper is a great player for a different plan, he isn't the 10 you want for this game plan.