Roseland, chopping both engines would be the action in the case if a tail rotor drive failure in the HOGE.
But they weren't in the hover I hear everyone shout!
Well, my 'opinion', based on the report, is that they were slowing to complete the pre-landers, or maybe slowing for a TRGB CHIP light. Anyway, during this slow down, the TRGB gave up resulting in a spin. 'Normally' gaining airflow over the fin would allow a flyaway, but what if the airflow over the fin wasn't sufficient to regain some form of yaw control?
What can you do? Try to get some airspeed on, while spinning, but it just isn't happening ... chop the throttles and where your right boot is, that's where you're going.
As I said, my opinion, and it's the best I can think of given the facts so far.