Probably because that would have spooked multiple countries nearby and started an outright war with Jordan, Egypt, Yemen, Qatar and Syria all piling onto Israel, which in itself would be disastrous. The current Israeli govt/IDF have been chipping away slowly during this attack on Gaza to see what they can get away with in the international community.
Whether a population is erased over 24 hours, a fortnight, 128 days or 75 years, it’s still genocide. That is what the Israeli Govt are doing to 2.2million people right now, 99% of which are innocent civilians.