Adaptations often follow the LN, not the WN, and the transition between the two can have drastic difference (see Overlord for example)
I'm guessing that scene might be cut from the LN because it either doesn't make sense in the long run or pushed down the line for better narrative pacing.
"aim for the crotch" is actually terrible advice in any actual fight. You want to disable (knee caps/elbows/etc), not cause pain. Because things can get people through pain, but mechanical failures are things you can't fix easily.