It's timed just not really contested, despite limited examples. Cadel has over a minute lead, in 90 odd kms it is very hard to make that up especially as the sprinters want their day in the sun. Not to mention that BMC has been a very strong team on the flat.
As for the limited examples, the commentators have only mentioned 2 examples and one of those was the second guy playing with the first guy; he stopped the attack on the second lap. To mention the elephant in the room, Evans lost by 2 seconds in the last couple of attempts. Everyone was very quick to remind him that they don't attack on the last day on that occasion. Especially Contador. I also seem to remember them waiting for contador on one of his recent wins when he had a bike problem.
Finally, there is drugs. Evans is widely acknowledged as clean. Last year's winner still has drugs hanging over his head. I dare say they realise they need the positive image of Evans as winner on the drugs issue.