Beoing's original FCOM
A couple of thoughts.
Firstly, the only bit in bold says that this event occurs "
during manual mode only". Perhaps, cognitively, the ET captain zoomed-in on this highlighted bit of text at 400ft climbing-out and tried to duck the issue by engaging A/P (if he had ever actually seen this FCOM). Not a defence, just trying to understand thought process.
Secondly, the FCOM specifically points pilots towards considering not turning off the magic immediately - "electric trim can be used to neutralise control column pitch forces before moving stab trim cutout switches". I'm not a 737 driver but one wonders how much time (MCAS iterations) one would spend trying to balance the forces before switching off. Prior to MCAS, did the NNC include this note?
PS. I tend to agree that leaving thrust at 94% (or whatever it was) would have brought increased complications.