If they (or PF) were continuously applying NU control input - and it obviously was not changing the situation - would they just sit there and not try something (anything) different - such as opposite (ND) control input? My concept of "logic" just doesn't seem to be working in this tale of tragedy.
The reason why they failed to recover? I don't know, even with full nose up trim full forward stick would have significantly reduced the AoA. One thing I am sure of though, when I ask Captains what the unusual attitude recovery recall is, I seldom get the right answer. It seems to me that everybody knows how to reject a take-off, deal with an engine fire etc. But I have never had unusual attitude recovery on a sim syllabus and because it isn't practiced most guys seem to forget it is there in the back of the Boeing QRH. Perhaps a similar issue with Airbus trainng?
Maybe the thrust being retarded to idle is a clue that somebody started to try and resolve the situation, but if so it seems hard to explain why full nose down stick wasn't maintained.