The whole point is to enforce rules that benefit the whole, at the cost of individual benefit.
Say you have 100 rials or 1M. Converting it to BTC might be good for you individually if you believe the local currency is going to lose value, but it’s not good for the collective as there will now be less demand and more supply of it. So the individual benefits at the cost of the group. Stopping that is the gov’s job.
This is a general comment, I am not familiar with Iran as a country and might be missing context.