Flawed Logic
The decision to evacuate is made by the Commander or next in command in the event of incapacitation, extending all the way down the chain to the most junior cabin crew member in the extreme case of a major accident.
With a wing on fire, it really is a no brainer. The logic (as has been reported) that the crew considered that fuel spilt on the ground and possibly igniting could have been a hazard to passengers, does not make any sense. The by far greater danger was the very real possibility that the whole aircraft could have exploded in an inferno at any time. It is not too different to the flawed logic used by the Australian B747 crew in Bangkok that "no fuel vapours could be detected in the cabin" as an excuse not to evacuate, when clearly the No. 3 engine had separated from the wing and fuel, hydraulic fluid and oil could have been discharging.
The passengers must have been terrified that they would be burned alive. That alone is a reason to allow them the option of getting out on the other side of the aircraft, despite the wind conditions and the possibility of having to dodge a few patches of burning fuel after coming down the escape slides.
The other consideration, is that they overflew a few perfectly acceptable airports on the way back, when in fact Boeing recommend to "Land at the nearest suitable airport" in the event of an engine failure on the B777.
Why did the cabin crew not use their initiative? Watching passengers take video for uploading to You Tube when at anytime they could have been in an inferno just makes no sense.