I think Cain had the oppertunity and skillset to finish, but he was afraid of matching up with an empty gas tank as preseving his was his whole strategy. On the ground and in the middle rounds, he never committed where he could have finished it.
That being said, I wouldnt fault JDS' BJJ from this. He wasnt there. By the time he was concious enough to be able to sub someone, he has zero in the gas tank. Not a think. He threw one or two punches but not even his mind was there. The only things to note to me were Cain's strategic genius and his lack of grappling skills versus his wrestling skills. He's stilla beast and JDS has good enough BJJ.