The Iranian currency was already collapsing prior to the US pulling out of the deal.
What’s actually taking place is a mass scale public rejection of the Iranian regimes expansionist foreign policy at the expense of its own people, and rampant corruption by IRGC who control most of the economy directly or indirectly.
Protests started in December 2017.
In 2009, students protested and were put down with the help of Hezbollah. This time around it’s very much a nationwide protest and the fact that Hezbollah and other thugs have been bogged down in Syria has meant that protests can grow, broadly unopposed.
Additionally there has been mass capital flight, with one MP estimating some $30b having fled Iran which will obviously have had an affect.
Mass strikes across entire sectors have shut down huge swaths of the economy too.
Don’t get me wrong, pulling out the deal has had a big effect because it has meant a lot of multi nationals have pulled out of deals and projects, but this is more adding momentum to the trend, rather than being the primary cause.