Well that’s just it, from here:
On the Airbus, when one pilot makes a control input (e.g. pulling back on the sidestick), the other pilot has no indication of this control movement Compare this to more traditional aircraft, which have control yokes in front of both pilots. On these planes, when one pilot moves the yoke, the other pilot’s yoke moves in tandem. If I hold full back stick, this is glaringly obvious to the other pilot. Apparently this is not so on an Airbus. In addition, when both pilots move their respective control sticks, the inputs are averaged. So, when the senior FO made an attempt to lower the nose of the plane, his efforts were stymied by the junior FO who was holding back stick throughout the descent.