But, a mistake you make in asking the question is two-fold, one - the Holocaust was not a lesson taught to Jews so they'll learn empathy. It was something horrible and traumatic that was done to them. Two - comparing the Holocaust to what happens in Gaza means you're not aware of what the Holocaust was. Maybe you know highlights such as gas chambers etc, but not what it really was (through no fault of your own I'm sure).
But, to attempt some semblance of an answer. In the same way you wouldn't ask Haitians why their gov did terrible things to the DR and their population - didn't they learn from slavery? Or about India/Pakistan, didn't they learn from the raj? Or any of the African states in conflict - didn't they learn from colonialism? Or Turkey and Syria, Iraq/Iran etc. Then why ask this from Israelis? I hope you get my rhetorical point.