It's a human weakness is that they can't fight their surroundings. They can easily be influenced by their surroundings, cultrually speaking. The Canaanites were practising children sacrifice to their idol gods. So if the Canaanites had the faith for the idol gods,
1. God would like to show that Abraham has a stronger faith.
2. The Jews are taught that God doesn't want children sacrifice. That's why in history children sacrifice is never part of the Jewish customs.
3. A scapegoat will be used in the place, who prophetically would be Jesus Christ.
Before the Jews were monotheists they followed the Canaanite pantheon of gods.
See Abraham's father who made idols.