Why do police officers get paid so much less than a professional basketball player?

Society rewards people in proportion to how much they value their services - so the contribution of police officers, firemen, food inspectors, highway maintenance crews, water works operators brain surgeons, nurses and so on are obviously more valuable than the contribution of sports figures. Then again a person who works more than forty hours a week to support his family in a low paying job know in his heart that he is worthless compared to a sports figure who earns more in year than he earns in his lifetime.