Given that there's just no logical reason for someone camped at Crabtree to be on that slope, other than attempting a descent shortcut, that's the reason I think the scenario Steve offered is probably the most likely. If John Lively's fall a few weeks back was for the reason the INFS believes, both summer fatalities on Whitney this year could be due to attempting to shortcut the trail.
I've taken some spontaneous shortcuts and been happy with the result, and I've taken others that left me wondering what in the hell I could have possibly been thinking. Either way, ascending or descending, it's almost always steeper and more intense work than staying on whatever established route.
Fatigue, hypoxia, impending darkness - I'm afraid we'll never know the "why".
And, regarding the TR quote I posted above on the north slope, I just want to point out that this was an experienced climber and mountaineer who had to exercise patient route-finding just to keep the descent in do-able 3rd/4th-class range. To me, this speaks volumes about the danger of that slope.
