It would be impossible for some of the cities to move inland not just because of unsuitable locations but because it would mean a loss of trade to many towns/cities. Kilika was a trading a town and the ocean was their direct means to transport and trade of goods. If they moved further inland this trade route would be blocked or made inconvinent. The same thing could go for many of the other sea side places in Spira (ship seemed to the fastest means of transport).