What would you do if you found out that a bunch of thieves were planning to rob your house? Will you leave your door open?
I can't explain it any simpler. When there has been multiple terrorist attacks on Iran's facilities using drones and micro-drones like the one on Bushehr power plant a couple of years ago that put it out of service; when Iran is being threatened every day with an attack on its infrastructure, etc. only a fool would ignore the threats and not think about defense.
Moving under ground is called passive defense.
- The most recent one in that list were Trump's (as reveled by chairman of the Joint Chiefs of Staff gen. Milley in at least 5 occasions the last of which [among other reasons] led to gen. Milley effectively removing his authority as commander in chief to prevent him from what he referred to as "pulling a Reichstag Moment").
- The other serious one I'd say was Bush's (as revealed by many including by general Clarke who says he received direct order from the president to destroy 7 countries [includes Iran] in 5 years).
- Last but not least the oldest was Carter's which was supposed to start with Operation Eagle Claw (aka the dumbest military operation in human history if you read to declassified documents released by Pentagon) to rescue CIA operatives from post revolution Iran to be able to follow that up with a full scale invasion and re-install the pro-US dictator.
Basically they are meant to ruin regular people's lives so that they revolt against their own governments just because US ruined their lives! After all that is a page from color revolutions.
They also work well in some cases, like in the case of Iraq. You see contrary to "documented assertions" the project called "invasion of Iraq" started at least in early 1990s in Clinton administration not in 2003 with Bush. The start was with sanctions. Why? To target the economy, create famine, starve people (I mean that literary, look up oil for food in '95), create unrest so that people revolt and from inside pressure the Iraqi regime to accept US demands making it easy to invade in about 10 years.
Now guess what those demands were? In short disarmament. Basically Iraq to give up its military capabilities, not WMDs no no, they knew very well Saddam didn't have any for example chemical bombs left from the days Germany+US+France were selling it to him to drop on his neighbor, Iran; but instead they demanded Iraq to give up things like ballistic missiles that could reach US bases in surrounding countries from which they initiated the invasion, the anti-ship missiles and fighters that could reach and sink US navy ships that were bombing their cities in 2003, etc.
Guess what were the main target in operations like Southern Watch in mid 1990's? Air defense mostly but also civilians. For example nearly 700 civilians were killed or wounded in one operation in 1998 to both soften Iraq air defense for 2003 invasion and also to create more unrest in Iraq.
Guess how did US bomb Iraq with 800 Tomahawks when the invasion officially began in 2003? With the USN and carrier groups that Iraq could no longer hit since the regime accepted the disarmament!
Now with a little bit of history, JCPOA can be seen in another light. Specially when you put that together with different US demands of Iran that had nothing to do with nukes but targeted Iran's economy, civilian sector and of course military capabilities just like Iraq's in 1990's.