The slot shows total trim adjustment. So if you imagine the whole horizontal stabilizer leading edge up then you can imagine how little the full back on the yoke elevators trailing edge up can do to counter it.
Probably just creates a pocket of turbulence.
Ok, so the whole huge honking thing is moved to trim. No separate trim tab. So manual inputs are overridden by the trim mechanism and the in flight computer. Probably the manual inputs pulling the nose up were forcing the nose down even further. The opposite of the desired attitude.