Reely,
Take a look at pictures of the wreck of the helicopter being craned off the roof.
It's smashed up underneath as much as the Norwegian one that hit the wires recently.
It came down very hard onto a tough and heavy roof that took a while to give way/finish collapsing. I'm sure a thorough structural discussion will be in the final report.
The witness statement of a "tumbling" crashing helicopter, if taken at face value, means that the rotors must have slowed substantially during the descent. Otherwise their angular momentum would prevent easy motion in any direction but yaw.