They did strike Iran to destabilize them around that time period and multiple times before and after the 2000s. Iran is also a much more difficult target than Iraq because they are (and were) much more powerful. Part of the point of the operations in Iraq and Afghanistan is not just to destabilize those countries, but to destabilize the entire region.

Iran is flanked on either side by Iraq and Afghanistan, having countries on two opposite borders collapse didn't leave Iran untouched. These actions are connected. Sure, I'm not saying they had everything planned out well beforehand, but they've had their targets planned for a long time and Iran wasn't even close to the same level of difficulty as Iraq and Afghanistan were. It makes more sense to go for the weaker targets and use these to weaken the tougher targets.