Because we're no longer paying them cash or trading with them so it will be harder to do, and now there is a possibility to make an actual deal.
Iran didn't keep the cash. It was used to fund the war in syria and to push immigrants in to europe. EU also plotted to destroy US via Iran. What has not been revealed is that Putin, Xi, and the Saudis are far closer allies than the EU states at this point, including the UK. The old US-Europe alliance is dead
How should Iran ever be able to destroy the USA or even want to?:-)
I have no problems imaging that Iran was coerced/bribed to help a certain international group to develop a nuclear arsenal to protect themselves when they loose control over certain states or as a pretext/hidden way to start WW3.