Originally Posted by kevin
I think it's because Marcus at some point in the film basically begins improvising because Khan takes his actions. He had an agenda that pre-existed but London and then the attack in San Francisco makes him change his plans a bit.
But what seemed odd to me was what Khan was expecting to have happen once he arrived on the Klingon homeworld.
In my opinion… Marcus didn't need Khan at all. He could have simply loaded the photon torpedoes on the Vengeance and carried out the mission himself in complete secrecy, leaving Kirk to be the fall guy when the Klingons came looking… like in Star Trek VI: The Undiscovered Country.