Why did the settlements in Ancient Crete have no defensive walls?

We are talking about the middle of the 2nd millennium BC. There was enough stone in Crete, the Minoans knew how to build, but they did not build walls, since there was no one to defend against, Crete is an island and in order for the enemy to get to it, a strong fleet was needed, and at that time only the Phoenicians had it. The walls were necessary for protection from the enemy, who had cavalry, siege weapons and chariots. Plus a large army capable of ravaging the city.