Saw the video on CNN last night, I actually found it hard to watch. Poor souls never had a chance going in at that angle. May they rest in peace.
Mere curious speculation:
I was thinking maybe an engine fire might have heated the wing spar to the point of failure? Didnt such a failure down a turboprop in Canada a few years back, after a landing gear fire in the gear well started from a brake dragging on T/O?