Here's a quote: "Pistachio trees grow to an average height of 10 m, desert trees, which explains why they live in West Asia. Pistachio is an edible variety of walnut. Pistachio trees also grow rapidly in high-salinity soil, about 50 kg pistachio seed crop, the largest producer and exporter in Iran. " From this it can be seen that the pistachios do not grow here next door, so it incurs a nice small transport cost. In addition, it is not very easy to grow and a single tree produces relatively few crops. Somewhere I also read that before a tree starts to bear fruit, it will take many years.