Weather does not look to be an issue. clear skys, day ops.
Fatigue may have contributed. Off body clock, long(ish) flight.
IMO, with no approach guidance they may have decided to complete a raw data visual approach with no auto throttle.
From my experience the 777 A/T is very good. Speed decay would not occur like this (viewing the speed alt data posted earlier).
So, they either decided to turn the A/T off for the approach or it was U/S. More like switched to be switched off as i doubt they would have dispatched with both A/T's U/S ex Seoul.
When you look at the speed vs alt data speed was within ball park approaching 600'. I am guessing they may have taken full flap @ 600' (or just prior) and left thrust at idle (manual thrust). speed was recorded at 85kts @ 120'!!! The stick shaker would have been activated shortly before this and this is when i am assume they attempted a go around? Manual full thrust, nose pitch up but it was all a bit late?? Kinda goes with what passengers reporting with engine noise.
None of this information is factual. Just my opinion on what I have seen and read so far.
Also out of interest, there was a 747-400 holding short of 28L. This could have been a disaster if they had speared left a little earlier.