A significant factor appears to be that the PIC had most of his experience in Airbus aircraft where the auto-throttle operates in different modes than those used by Boeing. The overall problem is the interface between humans and computers and deciding who/what has control and when. Why they continued to descend into the water when the pilot in the third seat kept shouting "glide slope!" is another question.

Yes, we glider drivers don't have engines, but we do have similar interface problems.

Mike