Because there is no world government. If US companies are barred from AI research then only China will have the capability of frontier-level defensive and offensive AI. And best of luck living in that world.

What's happening in Iran, if not world government?

How is whatever is happening in Iran related to a world government?

Are you calling Israel the world government? What's happening in Iran is on them.

good luck bullying a state that has ICBMs pointed at your cities.