I think there are only available for Iran people and transaction of bitcoin only there, if available for every one can buy and sell bitcoin with other country many people buy bitcoin with lower price on other exchange and sell with Iran bitcoin exchange account because have higher price, there are have big reason why Iran have different price bitcoin from other country, whats going on?
AFAIK, Iranian just can sell their bitcoin using localbitcoins, many exchange blocked by government in this country. So, if people not believe in USD anymore, using Bitcoin is kne of solution for people to save their asset.
About the price, anyone can set buy and sell as they want, if someone decide to buy even on high price, this buyer of course have a reason such as many people will follow to sell bitcoin higher, even this is just a speculation there. I don't think we can find a reason why iranian buy/sell bitcoin with $24K+ rates until someone know who the wallet owner.