Because they were on manual backup control they could not exert enough force on the controls to recover before Vne or the flutter speed of something was attained.
Airbus fly-by-wire. no force needed, it's just a "joystick". probability is though, in extreme flying situation - with obviously failing electronic systems (fly-by-wire will by design be the last one failing...) they possibly lacked the artificial horizon - you loose orientation completely. if you wind down in a 1G spiral, you can't detect this. if you happen to fly into a dense cloud with a paraglider, this is how you die. with no sight and no instruments in a rather rough condition, you're doomed. you loose orientation and thus control within seconds. a A330 needs something else tho get into this condition. but once you're there you're almost dead. within our neighborhood we had at least two planes going down in the past 10 years just like this. one was an F/A-18 fighter, the other a small-sized commercial plane. they flew directly at full speed into ground
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