Iran's nuclear deal, despite the obvious shadow it might cast on its sense of national destiny and independence among nations, accomplishes now what its nuclear objectives were. Why would the conservative, theologically rigid mullahs allow the civilian governing party to negotiate such controls over Iran's nuclear program?
The reason for Iran's negotiating now has three possible reasons: 1) the sanctions imposed by the West are too stringent and are weakening the ruling party's ability to govern effectively; 2) the dissolution of Iraq as a Sunni-led country has enabled Iran to create a servant government in Bagdad, a suzerainty of Shi'ite muslims who will create a safety barrier in the Eastern provinces of Iraq; and 3) Iran can wait its turn for acquiring nuclear weapons and take advantage of newer technology in 15 years. Of these three possible reasons for negotiating with the West, the second one seems most important.
Iran's significant armed forces are already embedded into Iraq's military in the efforts to counter ISIL in the northern provinces. Taking back Tikrit, with its oil production capacity, and securing Bagdad's dependence on the Shi'ite militias and the major portion of Iraqis providing the Shi'ite government's legitimacy, Iran is accomplishing its territorial ambitions quite well without nuclear weapons.
By dint of infusing Iranian military leadership on the ground against ISIL to support Bagdad's troops, Iran achieves a de facto Shi'ite Iraq. Iran supports the Syrian government, Hamas, Hezbollah and now the Houtis of Yemen in addition to its support of Bagdad's Shi'ites. Supposing that ISIL fails and its radical Sunnis disburse into Jordan, Saudi Arabia and Lebanon, which is a big supposition, there would be a significant realignment of Shi'ite and Sunni muslim nations within the Middle East. The United Emirates continue to be Sunni dominant and are aligned with Saudi Arabia and Jordan against ISIL and the Yemeni Houtis.
If Iran creates a puppet government in Sana'a to align with its pupil in Bagdad, the royal houses of Sunni conservatism will find themselves surrounded by heretic Shi'ite countries with ultimate loyalty to the mullahs of Teheran. In terms of religious demography, Iran will have achieved a much greater nation status than it could have hoped for with Iraq being run by the Ba'athists.