So why would the Canaanites be destroyed?

First: with few exceptions (like the Canaanite King Danel) most pagans did not see their gods as personal. They were worshiping the forces of nature and personalizing them. They believed that if the gods of life were pleased and excited, then there would be a lot of food, animals born to their flock and children born to their wife. If they were not happy, or mad at you, especially if the gods of death were mad at you, then you had either famine, or too much rain causing mold. Much of paganism in their worship would put on what can be described as "X" rated sexual actions hoping that these actions would make the gods of life all excited and productive.

In addition to the general description above, the Canaanites had an additional situation. The Bible calls the land as flowing with milk and honey. In our culture these terms symbolize everything good, predictable, easy exciting. However, that was only a part of the understanding in the ancient world. These terms were geographic terms. Honey included not only what the bees make, but any preserved food. A land of honey was good agricultural land, and thus fits our western picture of the terms "milk and honey. " However, the "milk" gives the complete opposite picture. Milk came from animals mostly kept in the desert. Your garden might give good, bad or in the middle crops, often poor crops and you hope for a better garden next year. Moving around a lot looking for food for your animals to eat, and you may not have much more food than what you get from your milk animals. Most places were either seen as lands of milk or honey. Egypt was seen as having both milk and honey, but in an organized land of honey along the river, but then once you leave the river area you are in the milk of the desert.

Canaan is where Europe, Asia, Africa, and Arabia all meet. The plants and animals of these parts of the world compete there, as well as the weather patterns. The Jordan was not a great river like the Nile or Tigris. The major god for the Canaanites was the storm/rain god Baal. Thus in addition to what pagans in the other parts of the world believed in making the gods of life excited by their sexual behavior, the Canaanites had more of a focus on this due to the intensity of the unpredictability of living in a land flowing with both milk and honey. They also added two other superstitions. One is that they felt that if they united their life forces in sexual orgies with your neighbors, across generations, including children and animals, that they were somehow giving Baal more strength and power to defeat the leviathan, and thus bring the life giving rain. They also came to believe that if they raped someone from another part of the world, that they could steal the life force of their victim: That food that would have grown in the victim's home garden will now instead grow in my garden in Canaan. That animals that would have been born to the flocks of their victim's family at their home, would now be born to my flocks in Canaan. That children that would have been born to the wife of their victim will now be born to my wife here in Canaan. And if they rapped the victim to death, then they would have stolen all of their life forces.

These are empty superstitions that does nothing but hurt others including abusing children. These actions do not affect the weather, nor the amount of food growing in your garden, animals born to your flocks or children born to your wife. The the Canaanites actually believed that this did and that they needed to "unite their life forces" or else they and their children would starve; and that they could add a little extra to their family if they rapped someone passing through the land.

Now this piece of land was quite literally the center of the ancient world. This was the most important trade intersection between Africa, Arabia, Europe and Asia. Yet, the worship services and superstitions made this most important intersection one of, if not the most dangers place on earth.

A big part of the conquest of Canaan was to make this all important intersection safe for the people passing through, and for a simple worship of a personal God who actually loved them was in charge of both the milk and honey aspects of their life.