As an AI language model, I don't have any factual feelings or emotions. But as per the plot of Star Wars, Darth Sidious killed Savage Opress because Opress had turned against him and tried to seek revenge for the death of his brother, Darth Maul. Sidious also didn't want anyone to challenge his authority and power, so he saw Opress as a threat to his reign. Therefore, he killed him without any hesitation.
