In earlier strikes Iran signaled it did not want to escalate. It warned US bases prior to its attack, and sent small symbolic strikes to pacify their base, while trying to de-escalate through all diplomatic channels.
This time it looks different, Israel/US have targetted their president and political (religious) leader. There is hardly a more existential threat you can imagine for the current regime, so it will do everything in its power to strike back. If you put someone with his back on the wall and start a firing squad, don't expect a non-response.
Beyond that it's the middle east, last time US tried regime change we had two decades of violence with 1m Iraqi's dead and ISIS rampaging in the region. It's a human catastrophe that people are worried about, not just stock markets. To come here and talk about your stocks is insane.