I'm not sure what you mean - Iran has been full-tilt pursuing nuclear weapons for decades. And America, its partners, and even its definitely-not-partners, have been working to counter that the whole time.
Remember that in much of the middle east, Iran is considered an enemy.
That Iran has been "full-tilt" pursuing nuclear weapons for decades doesn't make sense. Building a nuke isn't that hard, and getting the nuclear material is the hardest part. They've got that worked out. They've had the capability to do so for 20 years now. I defer to the intelligence community; they have the capability to build the bomb within about a year if they chose to do so, and are also not actively attempting to do that. (Until a few days ago at least).
Iran's religious dictator issued a Fatwa declaring nukes haram. This is why they've consistently stopped at 60% enrichment.
In a religious cult, everything rides on the leadership. He can't just come out and change his mind. He must have a very definitive reason that doesn't disagree with the reasoning in the previous Fatwa. His only real out is an existential threat where threatening a nuke becomes a tool to preserve lives.
Israel and the US have now given him that out. It remains to be seen if he actually takes it.
Remember that in much of the middle east, Iran is considered an enemy.