Because they still want us to open up a war against Iran.
Y'all remember "we will be welcomed as liberators" and "Mission Accomplished?" I do. We now have the following to add to this list:
if we carried out a targeted campaign against Iran’s nuclear facilities, against sites used to train and equip militants killing American soldiers, and against certain targeted terror-supporting and nuclear-enabling regime elements, the effects are just as likely to be limited.
Emphasis mine. Let's shorten that to the neocons' point: a US military attack on Iran is likely to have limited effect. They think that if we bomb, bomb, bomb, bomb, bomb Iran, there is a less than 50% chance that Iran will do anything in response.
Maybe the neocons have a hard time recognizing the fact that the United States is currently hamstrung trying not to lose two conflicts of which we are already engaged in the Middle East. While there is a serious lesson to learn about letting your enemies and rivals get away with bad behavior (appeasement), at some point, there has to be an intellectual grasp of reality. Sometimes you can't do anything about your enemies or rivals behavior because your own behavior prevents you from taking effective action.
Wars are expensive. Widening the conflict exponentially increases the expense. When you are already engaged in one conflict, it is difficult to project power into another conflict.
We are currently involved in two such conflicts, and it has proven difficult to extricate oursleves on our terms from both.
This is why you have to choose your conflicts carefully. It is why wars of choice are often called "misadventures." Engaging in conflicts, and then strategically drawing them out through bad planning and organization, limit your ability to engage in other conflicts. This is true regardless of the necessity of the other conflict.
Unless you're willing to mobilize your society for total war, which the neocons are decidedly against, because that would come with a political toll they are unwilling to accept.
This is one of the geopolitical result of invading a country of 30+ million people with only 300,000 coalition forces while at war with a seperate nation, population 28+ million people with only 290,000 coalition forces. Apparently, the west operates on a 1/100th scale force multiplier (and after 16 concurrent years of war with those two nations, we see how well that works out).
Now, the neocons want us to open up another war against a nation of more than 70 million people. And if that nation choses to respond with more than "limited effects," we're going to need a coalition force of at least 700,000 troops to achieve our current limited non-decisive goals. That's 700,000 in addition to the troops we currently have in the field.
Think the US population will be willing to ante up for that? Especially considering the results of our two current conflicts?
(HT: The Daily Dish)