Why wouldn't they? Bilateral trade agreements--Iran/Brazil, Iran/Turkey, Iran/others--would in part depend on it. They would have INCENTIVES to abide by it. U.S. policy, on the other hand, is driven by PUNITIVE intentions and ultimately by the great thirst of the U.S. war machine for more and more oil, and its established pattern of sanctions/heinous war. Iran is independent, and largely peaceful*, with no evidence of territorial ambitions, and furthermore with a long history to worry about, of egregious U.S. interference, and the recent horrors of the U.S. war and occupation right next door in Iraq, to make them fearful of, and defiant of, U.S. goals. They have absolutely no reason to believe that they are safe from U.S. interference and U.S. attack. They have absolutely no reason to cooperate with us.
As for "they can be penalized as well," I think that this U.S. blitzkrieg to punish Iran for its independence may well turn out to be a UN-destroying action--much like the U.S. embargo of Cuba is destroying the OAS. The "third world" is fed up with this tyrannical U.S. behavior. There is a proposal on the table in Latin America to replace the OAS with a Latin America-only institution that excludes the U.S., following upon a trend in various events over the last few years whereby Latin American leaders have gotten together among themselves--in UNASUR, in the Rio Group and other organizations--specifically excluding the U.S., to solve problems largely created by the U.S. In other words, U.S. behavior is leading to the increasing irrelevance of institutions in which the U.S. wields far too much power, on the side of multinational corporations and war profiteers.
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*(It's interesting that the police in Iran shoot one demonstrator and there is no end of corpo-fascist vilification of Iran as undemocratic and inhumane, and the Israeli military shoots and kills at least nine unarmed peace activists, on an unarmed ship, with possible additional deaths that were thrown overboard, and our corpo-fascist press--at best, AT BEST--treats it like a P.R. mistake, and fills the airwaves and the print press with EXCUSES for this horror.
http://news.scotsman.com/world/Gaza-flotilla-deathtoll-39higher-than.6340319.jpAgain, the police kill one protestor in Iran--something that has happened in numerous western countries, including here--and Iran is painted as evil, dictatorial and a menace, yet U.S.
allies, guilty of far, FAR worse, anti-humane, anti-democratic crimes, including but not limited to Israel and Colombia, are given every benefit of the doubt and constantly supported in their excuses and justifications for their plain crimes against humanity--and U.S. crimes against humanity, including widespread torture of prisoners and the slaughter of a million innocent people in Iraq, to steal their oil, have already passed into the corpo/fascist 'news' monopoly "river of forgetfulness."
Hypocrisy, writ very large, indeed!)