The US does this because Israel exists primarily as a weapons platform for the United States to maintain control over regional resource extraction. Israel does this because their political leadership wants to achieve their dream of a white ethnostate.

Because the indigenous Palestinians keep reproducing and have nowhere else to go, Israel has maintained a state policy of periodically reducing the Palestinian population with the goal of driving them to eventual extinction as a population. For years Israel would euphemistically call this “mowing the lawn”.

The United States and liberals in the Israeli government would prefer that Israel carry out this extermination slowly to mitigate the risk of international interference. Conservatives in the Israeli government would prefer to exterminate the Palestinian population all at once to prevent any possibility of internal resistance. As conservatives now hold power in Israel, state policy has favored more aggressive campaigns of expansion and depopulation. The US vetoing ceasefire resolutions at the UN is part of preventing international interference in the extermination campaign. The US can then maintain control over the rate of the campaign by adjusting the flow of weapons it provides to the Israeli government.