I do believe this is due to idea of goodness and honor. If a man was a good person, it would show in his physique. Read any literature from the time and you will time and time again see the good men described as good looking and in good physical shape. Look at Odysseus! He is described as a good looking man and in great shape. Even when faced with Utopian civilization, he is stronger (with some help from Athena of course). This also translates to Greek Olympics where being the most in shape and intimidating would earn you massive respect. Some men would forfeit by just looking at their opponent. Winning the Olympics meant you were taken care of for the rest of your life. Some city-states went broke taking care of their successful Olympians. This is not my speciality though. This knowledge only comes out of my minor in Classical Civilizations.