In my oral board they interviewed around 75 people and only invited 15 or 16 to take the Physical Test so don't feel bad. They also asked me why compassion (among other things) was necessary for police officers to have. Nothing was wrong with your answer. Maybe you just don't have the life experience they're looking for. Maybe other applicants were more qualified. It wasn't necessarily your answers.
In life's small things be resolute and great
To keep thy muscle trained: know'st thou when Fate
Thy measure takes, or when she'll say to thee,
"I find thee worthy; do this deed for me?"
Nemo me impune lacessit.