Huge vast swaths of Australia and the United States are effectively deserts, but they don't "define" the country. It mainly comes down to what pictures you see in the news when something happens, and Iranian cities look "deserty".
This is the real reason, and I am guilty of it, it's because of the Persian cultural influences and some pictures, people just assumed, it wasn't until I saw some travel shows or more social media that I realized its closer to what I saw in Turkey.
