Iran has seen what happened to Libya and Qadaffi when they surrendered their missile and fissile development program.

There's also the Iraq/Hussein cautionary tale. We told Hussein he had to get rid of all his WMD's, and he did get rid of them. But then we invaded and overthrew the government anyway. It's impossible to prove a negative, particularly to someone who is determined to believe you're lying about it.

It's the folly of trying to have "Iran never gets a nuke" as the objective of this war. If you believe that Iran can restart their nuclear ambitions without being detected by the IAEA (as Trump clearly does, given the abrogation of the prior agreement), then how can you ever know that you're getting an enforceable promise from them? And if you don't believe that you're getting an enforceable promise from them, what assurance could they ever have that you're not going to one day just decide they're lying and have a secret program?