Let's say they went around for Windshear. As they pull up, they meet a greatly increasing head wind component.
The GA starts, and from what I've read, a 737 pilot has to push, and trim forward, especially with a light a/c.
So: pushing forward, would make the THS trim nose down on a 737? (it does on the non-Boeing type I fly).
Full power causes nose to rise due to engine thrust line below the wing, so more nose down trim to stop it rising too much.
Extra energy from increasing HWC, would tend to need nose down trim as ROC increases as aircraft meets rapidly increasing headwind.
Generally high ROC with full power and while hand flying might cause PF to trim forward to reduce the ROC.
Reaches GA standard level off alt.
As they level off, thrust comes right back, reducing that upward thrust moment, and causing the a/c to go nose down with THS already almost full forward, nose down.
They are IMC, so miss the gravity of the situation for a few seconds (some distraction or other).
Big ROD develops.
Come out the bottom, see the ground,but too late.