To aid their kill speed...introducing...
Death-dealing.
Increases proc chance for sh/sh2 and increases damage dealt

Observing Abandoned Town skeleton fights has led me to believe that the problem is...
You are attacking wrong target.
Yes, game's RNG is bit less than totally random
Yes, some fights might go by with you never getting any crits/other things in whole room
Yes, that can also affect how often and how much damage you do with SH (by almost 50%)
Yes, changing target if things don't work can speed up room's killing speed by 30%

Game generates random numbers and uses them in order it needs them, for you and monsters and everything. If you don't like your end result of every nth number, you can change your position in said random number queue by fighting different target.


Above is not necessarily based on reality, things can get scetchy when staring at screen for long times. It is based on multiple hour+ sequences of f stays in said place
And yes, I'm bored.