To all the techies who want to have infallible systems.
The autothrottle received a signal from the radalt to go to flight idle.
The crew apparently didn't notice.
Imagine if
The throttles were in flight idle (normal early in the approach) and then just 'dropped out' of its own accord (it happens) so did not apply power when needed.
The crew did not notice.
The effect in both cases is the same.
Why the autothrottle failed to apply power is not immediately relevant to the accident
The crew not taking action is.