The US desires were completely untenable. Saudi Arabia hit the Hubbert Peak in 2007. Oil is going away. Iran wants the ability to pursue energy independence while also counter-balancing Israel, which tends to act unilaterally.

People think the US has been enemies with Iran since 1979. It's more accurate to say that Iran and the USA have been engaged in a cold war in the middle east. Israel and Pakistan (and formerly Iraq) have been our proxies, while Iran has had Hamas and the PLO. The deal basically daylights the clandestine combat between the two countries, thereby deprecating proxy warfare and normalizing relations.

Part of the reason we didn't get all we asked for is we're in a losing position. The Sunnis are going batshit all over South Asia while the Shia are consolidating power and looking reasonable. The Iranian regime is a zealous and reactionary theocracy but the Iranian people are progressive and young. It's exactly the sort of situation where anyone clever would export a hundred billion dollars worth of Ford, McDonald's and Taylor Swift and let the millenials sort it out. Simply and frankly put, Iran is missing a generation from the Iran/Iraq war and the millenials aren't aligning with the Ayatollahs.

Iran, post-fundamentalism, is going to be the driving cultural influence for the entire Middle East. We can fight that or we can be friends with it. Being friends with it is a hell of a lot easier, especially when you consider that Iran/Persia hasn't launched a war of aggression since the Sassanid Empire.