The only reason they don't is because they're afraid of losing the Western support they depend on entirely. Doing so would be genocide. Right now they can dance on the line and say they aren't and it keeps the pressure on their allies low enough to be tolerable.
As @Plasmodium says, they're playing the long game for the land. Slowly seizing village after village in the West Bank, neighborhood after neighborhood in Jerusalem (they just took out a section of the Armenian quarter the last few days), and finally, slowly choking the life out of Gaza until the people leave, die, or fight back hard enough to justify total elimination in the eyes of the western world.
The ridiculous thing about you guys pretending this isn't about ethnic cleansing is that Israeli's are pretty open about it. The Knesset is filled with people who call for ethnic cleansing. The IDF protects illegal settlers who commit acts of violence to seize land in the West Bank and Jerusalem. The political messaging by the Israeli government is totally different in Hebrew than their English propaganda for Western audiences.