Why are Iran's largest cities rarely by the coast?

I think large cities in Iran grew not because of trade by sea, but for other significance. For example Shiraz has historical significance and good weather. On the other hand Iran does not have much sea borders (compared to land), so on the matter of trade it relies on land more than sea. In general I think major cities and mainly the Capital of every country is developed more based on political reasons than trade.

Iran has chosen it's capitals based on political strategy and development. It's current capital, Tehran, was chosen  because the government (then under the Qajars) wanted to remain close to the then Iranian-occupied, rebellious Caucasus region. Additionally most of the other major areas were occupied by power-hungry family members of the previous dynasties. There was no defensive reason behind it, in fact the Mongols had completely destroyed Tehran in the 13th century. But that was only from 1796 and onwards, and was the 32nd capital. Before it was Tabriz, Tehran under the Safavids. Tabriz was chosen because of its strategic placement near Turkey and because of its prior high level development. Tabriz was the center of trade in the Middle East at the time, and a major Silk Road post as you had to pass through it in order to get to Eastern Asia. The majority of the population was already there, and the Safavids saw no reason why they should not place the capital in their most thriving city. Now I cannot go through all 32 capitals and the reason they were chosen. But in general, all Iranian capitals were chosen for 3 reasons: The city boasted high levels of development and were centers of trade (usually on the Silk Road) The city was in a politically strategic location, where only the ruling faction had power or was situated near regions that threatened to break away The city held high levels of cultural significance 

Better climate, perhaps including malaria in some cases.The Gulf is extremely hot.https://en.wikipedia.org/wiki/Shiraz was a major trading city and not too far from the coast though not on it.Mexico was another early modern state where merchants lived in highland Mexico City and spent only the minimum necessary time in hot, unhealthy ports Veracruz and Acapulco.