Why does nobody else follow up on the UN resolution from 1948?
(Just like in the case of India / Pakistan UN decided to divide the area into two parts, one for Jews, one for Arabs.)
I can also ask: why does so few other support the single somewhat functioning democracy in the region?
Then, on to your question: After initially being supportive of Israel, USSR took the other side early on and propped up the surrounding nations with weapons so US was kind of forced to do it.
Later on it has turned out to be a beneficial although controversial deal for both parts.