It could be that the crew thought that they were coupled to a glide path that was in fact out of service OR that they had not selected correctly on the auto throttle/auto land or that they were just really damn tired and unable to function. It is more than likely that they had been awake for possibly 24 straight hours when you count the time from when they left home/hotel until the time of the accident. They had flown all night, in the dark or twilight on the northern great circle and found themselves having to perform the most difficult part of their job just when their bodies were telling them it was bedtime back home. I have flown many a Red Eye and I guarantee you that you are not at your best after a 12 or 13 hour all niter. Think about that the next time you jump on that 14 hour non stop from LAX to Sidney or even worse the non-stop from Singapore to JFK.
There were two pilot crews (two people each) and each had a shift during the flight.
There were “four” crews that alternated during the trip.
All airlines had been notified months ago that the glide path thingy was not working on that runway.