The other reason is that the FD would have been taking it's information from the selected values, correct? According to the trace, none of the "Selected V/S" values during HN39's excerpt even come close to requiring a 15 degree NU climb.
Here I don't agree,
pitch bar guidance is limited @ +/-22.5° of pitch, 50° FPA, if that limit reflects the +/-6000ft VS limit it would be definitely above 15°.
Once again this is
IF!! not VLS protected.
@CONF and Lyman:
I've lost control of the aircraft
At that time it was already in fully developped STALL....a negative climb state!?
If he was following the guidance he would have released the SS and even pointed the nose down between (02:10:55) and (02:11:05) in HN39's graph instead he went back to 15 pitch°