The US is when you’ve dominated the map militarily, neuter the other civs instead of sacking them, and then spend the rest of the game uncontested getting the cultural victory for the lulz.

I’m convinced the answer is “Israel absolutely has nukes and will use them if we stop providing them conventional arms”

But the real answer is probably as mundane as “They are the core of US power projection and intelligence gathering in the middle east, and we really don’t want to lose that level of influence in the region”.