So what, he didn't wear a helmet.
This is flying-not cycling.
High G impact, lots of water, temporary unconciousness from shock, all that mud, any of these could kill you, no matter if you've got a helmet or a bloody scuba suit on.
Dale Earnhart Snr had a helmet on and still broke his neck- but that was ok, his head was saved.
Fact- Do something dangerous for long enough and eventually the danger will catch you, your fault or not.
The tragedy is that he is gone and the industry has lost a leader.