The threat of international condemnation and the less hawkish members of the Israeli government and electorate.
Predictably the rate at which civilians in Gaza are bombed by Israel went up not down after Hamas' acts of terrorism the other week.
Even if you believe that the Israeli government is ontologically evil; serving them up causus belli to bomb and potentially invade Palestinian lands does not constitute "preventing Palestinians from being exterminated", rather it actively helps them hastens the process
The Hamas and IDF aligned telegram channels have both been remarkably consistent about cheering when about our munitions landing in their territory and decrying the reverse.