You can only conclude that they were unsufficiently trained to recover from a stall.
well, to recover would be the next step , but when i understand it right they all did not even realized they are in a stall.
its not a forum,s job to blame the crew but we have to remember , all this happened out of a level flight with a constant Speed and altitude - with a stabilized and properly trimmed aircraft.
so of course doing nothing beyond maintaining altitude and wings level would be much smarter then just giving a full pull on the yoke and so forcing to stall. the question why he did this will never be answered i guess.
further its confusing not to realize it for several minutes by three people - when you have 20 deg pitch up but go down like a rock - what could it be other than a stalled condition ?
some might think that any ppl holder would have realized and managed it better and so Coroners start to blame the skills.
i have to give a point that in this very particular Situation - blocked tubes, stall inhibit below 60 kts - the design of the System might have further confused the crew, but this Situation is so dramatically out of any flight envelope of this aircraft and you have to make such fundamental piloting errors to force an airliner into this situation that not even Airbus thought of it designing the stall warning system.
best regards