Awair,
Airbus has had similar problems with pilots not switching off both FDs before approach etc. Airbus has now redesigned in A380 and subsequent A350 models have only 1 button FDs on/off in the middle of the Glare shield FCU panel.
But still doesn't explain dropping off the approach path and not correcting or giving it away earlier.
We're the pilots monitoring:
1. the approach path PAPI
2. Airspeed
3. Attitude
4. Runway alignment.
Even if your stabilized at 1000 feet and it all looks fine. Below 1000 feet if any of these parameters are grossly out a GO-AROUND should be accomplished, as soon as its recognized. Automatics or no automatics.
So if they weren't monitoring the approach what were they doing?
CVR may tell.
It was a SKY BLUE DAY! Tantalizing sites San Francisco Bay,
one wonders.