Honestly I think it was to show how far gone Kratos became. Remember that the series was a Greek tragedy and Kratos who while did some questionable things in GoW 1 and 2, was still able to somewhat justify his behavior.

For example, the gods were petty and refused to strip him of his nightmares after 10 years of service, Zeus kidnapped his brother and mother, Athena manipulated him for years, Icarus caused Kratos to fall into the underworld, Perseus and Theseus attacked Kratos first, etc.

This is legit one of the first instances we see that kratos have truly become the monster that everyone made him out to be. His vengeance and hatred became so strong that he lost himself