bear/ChristiaanJ:
I don't think cowardice or even fear enters into it. I think training, experience, and how one is rewarded for one's actions play into this idea, even if the idea is a guess, or even if it is wrong.
Given
that the pilots in the cockpit had briefed with the Captain about the rough Wx ahead
Given
that they had made a course alteration (~12 degrees) to avoid rough(er)weather
Given
the crew had discussed that a planned climb could not be achieved with parameters (temp) as forecast and originally planned for
Given
this is the ITCZ with significant vertical development in the weather
Given
The crew also discussed the turbulence, and expected more, possible more robust turbulence in the next period of time based on their latest radar scans (of whatever quality, good or medium or poor)
and
Given
Pilots are trained to not fly in the upper two thirds of a thunderstorm (and if what they saw wasn't a thunderstorm, it was certainly non trivial convective activity, which you might usually treat with caution similar to CB's when you carry passengers for a living)
THEN
the pilots could be of a mind to NOT descend into the turbulent air (good thinking, on the face of it) though that does not require that one climb.
JD-EE guess is founded on the idea that concern about meterological factors was near to the front of the PF's thoughts as he worked through the "Hi, I am ALT 2 Law, latched, you have the controls" flying problem. This might be considered a compatmentalization issue, and be a productive line of inquiry for pilot community consideration and lessons learned. Trouble is, there isn't all that much evidence to support this train of thought.
As before: the pitch and power chorus, and the "maintain straight and level as one troubleshoots the UAS problem" chorus, are right.
Had those issues been his sole priorities, we'd not be having this discussion. Not a matter of fear, perhaps a matter of ordering the problems to be solved in the time available. (Won't digress into how the PNF can help with all this, it's his skin too ...)
That said, weather is always a factor in flight, and bad weather moreso. The worse weather gets, the more of one's concern and attention one tends to give to it.
At least, that is my experience.
Nothing to do with scared, coward, brave, none of that.
Typical pilot concern for the weather, and in this case, bad weather.