Like American soldiers in the second world war, their better diets makes them larger and stronger than their opponents. They are better trained and equipped because their leaders actually give a **** about them rather than treating them as disposable equipment. And they have far more personal initiative because it has not been brainwashed out of them in the reeducation camps.
The US had "reeducation camps" also during WW2. My grandfather told me some strange stories of the brainwashing that went on during Ranger training back then.