The reasons for the water landing are inconsequential here. From my time as a waterbird instructor I suspect the a/c suffered serious hull damage (hitting the water at that speed and height) and even for the few seconds it was on the deck, 1000's of gallons of water would have entered the front of the hull adversely affecting the fwd C of G with the very tragic consequences.
I'm at a loss to understand that given that the helo survived the landing and there was a ship 100 metres away, that the pilot did NOT elect to shut down and evacuate an otherwise intact airframe. There would have been no loss of life in that instance.
In my experience, within seconds, the water would penetrate the avionics bay (fwd) and knock out the stab systems causing aggravated control inputs in an already tenuous C of G situation. This together with the bow wave drag - determined his destiny. Sad really.