Because you're always looking about a comparison, a choice. Holding the world economy hostage placates some egos at incredible cost to Iran ... or agreeing to the US commitments, problems and all.
Iran is already under decades-long sanctions and have shown that their ability to wait out the US+Israel was massively underestimated.
After Vietnam and Afghanistan, has the US not learned that countries at war are willing to incur costs well beyond what the State Department thinks they should?
