Why are American politicians so comfortable supporting an ethno-state even though the US is not supposed to support apartheid regimes? Why is the US administration now so willing to throw US allies (Japan, South Korea, NATO members) under the bus with a 1970s style energy crisis to save 1 country of 9 million from a war they single unilaterally started?
Finally, to answer the OP's question: * Israel is facing an existential threat; the US ending the war means de facto end to their state; * US - not allies as that requires mutual consent to wage war; see above text for actual real power relationship between Israel and the US