I agree, cooperation is what is needed not blackmail. That's what the sanctions are doing: if Iran wants to cooperate economically with other countries, it needs to stop trying to blackmail other countries with threats of nuclear strikes.
As far as why, Iran regularly threatens to wipe other Middle Eastern countries off the map - including the nuclear armed Israel, which would easily trigger a nuclear war in the middle east. The simple reality is that there is not an equivalency between the possession of nuclear weapons by China, Russia, NATO, versus North Korea and Iran. The former don't go around threatening to wipe other countries off the map on a regular basis. Nor does Israel, they don't even officially acknowledge nuclear capacities. The latter do, and in North Korea's case it has created one of the most infamous geopolitical catastrophes of the 20th century. And Iran stands to become a much larger North Korea in a much more volatile part of the world.
1. https://en.wikipedia.org/wiki/Iran%E2%80%93Israel_conflict_d...
Then there's all the hits on people by Mossad.
Why would a government who doesn't care about its population look at the suffering of those people and change course? Are we naive enough to believe that the Iranian elite aren't circumventing these sanctions personally?
Finally, why? Like, after hundreds of years of imperialism and political interference, I've yet to hear a compelling case to continue doing these things given they've done nothing but push us further away from each other and closer to a climate-crisis, dystopian nightmare.
We need cooperation not blackmail.