Strategypage writes:
The U.S. is trying to find out what Iranian intelligence operatives are doing in Venezuela. Iran denies that their people are in South America, but the U.S. is convinced otherwise. The leftist leadership of Venezuela has become an ally of Iran. The U.S. is also concerned about the thousands of North Koreans working in Iran (and Syria). Many of these North Koreans appear to be technical specialists, working on military projects. Sanctions have halted the shipment of most military goods to Iran, but not the movement of people.
So even if we destroy everything in Iran, nuclear and missile programs would survive abroad to be brought back to Iran to resume--not start over from scratch.
Remember that when we struck back at al Qaeda for their 1998 East African embassy attacks, we not only destroyed tents in Afghanistan, we also hit a plant in Sudan we suspected Iraq and al Qaeda were using to make nerve gas. Way back then we figured Iraq was dispersing WMD programs outside of Iraq where they were theoretically subject to UN inspections.
Of course, that was back when it was OK to speak of Iraq, WMD, and links to al Qaeda without being accused of lying.
Still, Iran's rulers may be nuts but they're not stupid. They know we can attack them. So they take precautions to minimize our strikes, like digging deep or siting near civilian targets. Outsourcing weapons programs to trusted rogues is another way to do that.