For the same reason that attacks are up against Israel. when you look at the numbers killed in this fight they pale in comparison to the atrocities that Hamas and organizations like it have committed against arab populations in the middle east. They are singled out because they are more widely reported as Israel does not limit free speech or the press. Israelis are more critical of their own government than even say....you.
This is only because the goalposts were moved to make a more convenient point for defenders of Israel: if you lump all arabs together and add up all their crimes, and since Hamas is arab we can say that Hamas has caused way more death and destruction since well, they're arab so we should probably count Saddam's crimes, Assad's crimes and all the crimes committed by secular dictators against their Arab populations along with all historical terror operations across Lebanon, Syria, Jordan, Algeria, Israel and every other country in the middle east.
Now if we add all that up then Israel sure looks good right?
Only if you agree with all those crazy assumptions you had to make to end up there! This is another bit of enabling-psychology that polishes the Israeli self-impression of righteousness - and is dangerous in the way it conflates independent reasons for violence from disparate and conflicting forces across the middle east as one monolithic entity of arab violence... sounds to me vaguely prejudiced actually, to even consider thinking along these lines...