IMHO the ignorance of the audible stall warning could only be caused by the pilots assuming, that the stall warning would be triggered by too low speed (instead of AoA).
Speed incorrect -> Stall warning -> ignore it
When the speed came back they had stalled the plane and the speed stayed low => assumption: still incorrect.
Why should they believe now, that the speed was more correct than before?
Why should they believe with all this confusing stuff around them, that any other indication was more correct?
The speed even became lower and lower and the stall warning disappeared at some point. -> continue to ignore all this
It remains the question: why did he pull so much? where is the no speed indication check list, and so on.
Also: pitch is not AoA!