Stab ND
When flying the MAP manually with a relativly light B737, one easily might apply to much ND Trim in attempting to capture a low level-off altitude. Since the speed might increase rapidly one can find himself in a condition with Stab Trim at 0 / Full ND and T/L retarding to more or less idle.
What may come next is what the second video shows in its late stages. My company had a very very close shave with a 735 years ago going around, they lost more than 1500ft after the initial level off and were pulling as hard as they could....
It might be difficult to realize the condition one is in and the existing setting. And more difficult to make the next step and increase thrust to get rid of the impressive nose-down moment while retrimming and - probably most of it - being puzzled.
Add adverse weather and gusty conditions.
In any case interresting to see all the speculations above showing a total lack of 737-knowledge, not speaking of experience. Let's all hope those don't come from pilots.
And let's hope none of us ever gets caught flat-footed like this. It's always waiting just around the corner....