Trimming out the control forces is an instinctive and unconscious action that 737 Driver has so nicely articulated that is a fundamental skill that pilots with 5 hours of flying time have.
This statement is exactly why I feel that we do not have the complete picture yet. When the trace shows that at least two different pilots did something completely counterintuitive (a few short bursts on the trim rather than holding it down) when they really, really wanted to make the plane go UP instead of DOWN, I think that there is a factor that we do not know about yet. I can't imagine anybody not continuously holding the "UP" switch when they see ground in the windshield, it is just not the way humans operate. You can see Formula 1 drivers adjusting the steering wheel while their car goes airborne, people try to turn on the lights when the power is out, the helmsman will pull on the throttles as the ship with dead engines inexorably heads to crush the wharf, etc. It defies reason that none of the four pilots held the button down to the last.
I don't know what it could be (can you break the switches by pressing too hard on them?)