Q:

Why did this Cirrus deploy the parachute while ditching over Pacific Ocean?

In this incident near Hawaii, a Cirrus SR22 had fuel problems and deployed its airframe parachute.
My question is why did the pilot deploy the parachute rather than perform a "normal" ditching procedure in the ocean?
For reference, here's the video.

A:

Once your engine fails the airplane is the property of the insurance company, your only goal at that point should be to survive. Using a whole-airframe chute increases your chances of survival whether over land or sea. 
The things that kill people in forced landings of any kind are high-g deceleration and post crash fire. A parachute decreases the chances of both as you have very low lateral speed and much less chance of fuel tank leaks. A parachute also will increase the chance the airplane will remain upright, so escaping the aircraft will be much easier - very important in a water landing!
The only reason for a "normal" ditching procedure is that you have no other choice, using a parachute if you have one will almost always be the right option. The only time I would consider otherwise is if I had enough altitude to glide to a safer emergency landing spot. If pulling the chute would mean landing in water or dangerous terrain but gliding would mean reaching land where a forced landing was reasonable I'd probably opt for gliding.  

A:

First, according to one operating handbook for the Cirrus SR-22 (there are several versions out there), pulling the chute is the correct ditching procedure (CAPS is the parachute system):

Ditching

Radio ............................................ Transmit (121.5 MHz) MAYDAY giving location and intentions
Transponder...........................................................
  SQUAWK 7700
CAPS .............................................................................
  ACTIVATE
Airplane.........................................................................EVACUATE
Flotation Devices ............INFLATE WHEN CLEAR OF AIRPLANE

Second, the conditions were reported to be windy with high waves:

Weather conditions at the time of the rescue were seas of 9 to 12 feet
  and winds of 25 to 28 mph.

Those would be tough conditions for ditching in. I've read several times that when light aircraft ditch, the pilot and passengers usually survive the impact but they often struggle to exit the aircraft successfully. This article and video explain in detail how difficult it can be to exit an aircraft in the water, even in good conditions. If the aircraft flips or cartwheels then exiting would be extremely tough and the rough sea would make it much worse. Since the parachute lowers the aircraft straight down in a more or less level attitude, the chance of flipping over is greatly reduced. The downside is that you no longer have control of where you touch down relative to the waves, so you might land just in front of one but that still seems like a good option compared to the risk of flipping the aircraft on impact.

A:

Maybe pulling the chute is the normal ditching procedure for a cirrus with an airframe chute. The splash down looks to be very gentle compared to a normal gliding ditch with fixed gear. It's also less prone to pilot error; once you are dangling there is not much the pilot can mess up.
I imagine the checklist being something like:

pull chute
when aircraft stabilizes open door put on life vest and prepare raft
should plane roll and sink get out and on the raft

