And then they got new intel. Iran is also the primary sponsor of international terrorism, and the entire EU is aligned on sanctioning Iran. I know history of western intervention in the Middle East is full of terrible mistakes, but that doesn't mean we should turn the other cheek. I'd argue we've been to lenient on that front, in many ways.
I don't want us directly interfering in the Middle East, but I also don't want us supporting regimes that are diametrically opposed to our own ways of life. And sanctions are the way to do this.
The reason the US acts the way it does in the US is not based on any immediate logic. There's a great paper, "Rebuilding America's Defenses" that describes US foreign policy in extremely straight forward language. It was written during Bush's era, but many of the people with their names on it are part of the effectively permanent political establishment.
Their goal was (and perhaps if they're delusional - still is) to maintain hegemonic control over the entire world. The main motivation for things like attacking Iran is 'projecting force.' It's supposed to work to intimidate other countries into deference and compliance without having to actually get involved in a battle with them. Basically mimicking how school bullies work.
So you're looking for a reasonable explanation based on superficial pretexts, but there is none. The same is true of Iraq. It's not like we really thought there were WMD. But it was simply an opportunity to project power and keep the military industrial complex churning.
I don't want us directly interfering in the Middle East, but I also don't want us supporting regimes that are diametrically opposed to our own ways of life. And sanctions are the way to do this.