From my experience the 777 A/T is very good. Speed decay would not occur like this (viewing the speed alt data posted earlier).
...Unless, as has been mentioned above, the A/T is in HOLD mode, in which case A/T Wake Up is not active.
As there was no ILS, they may have been descending in FLCH or VNAV SPD, conditioned by a thousand ILS and RNAV approaches to expect the A/T to take care of the speed, for it to just stay at idle.
I've had students come to their upgrade with thousands of hours on the type, unaware of this "feature' of the AFDS.
ETA- Crossed posts with Douglas, who's quote summarizes it very well.