They should ask the Israelis.
It was, after all, Israel’s leaders who insisted that the nuclear file be addressed first and on its own, and who pushed back hard against any attempt to forge a more comprehensive understanding or grand bargain with Iran (an idea explored over a decade ago in back-channel talks during the term of President Mohammad Khatami). Last summer for instance, when Iran and the West found themselves on the same side against Islamic State (also called ISIS) in Iraq, senior Israeli Minister Yuval Steinitz, who was head of the Iran file at the time, noted that Israel had pushed for and received commitments from “the Americans and the British and the French and the Germans—that a total separation will be enforced,” that is, the West would not negotiate with Iran on regional issues until the nuclear question was dealt with. Israel, in other words, demanded that the nuclear file be treated as a standalone issue—the very thing that it now criticizes about the deal.So writes David Levy at Foreign Affairs magazine. The point is that Israel did not want to risk a rapprochement between the United States and Iran, a prospect that could water down Israel's influence in the United States and in the region.
Iran had offered a comprehensive grand bargain to the United States in 2003, in which all outstanding issues would be discussed, including Iran's support for the Palestinians. Indeed, as part of the proffered grand bargain, Iran accepted Saudi Arabia's previous Arab Peace Initiative (2002, renewed 2007), which would have included recognition of Israel in a two-state context. President George W. Bush gave Iran's overture the back of his hand, having branded Iran in 2002 as a member of the Axis of Evil along with Iraq and North Korea. (This was a fine thank-you for Iran's cooperation after the 9/11 attacks.)