I think the dogs run because they person's body language is either negative or they are acting like they want to play. Most of the time when a dog is being caught from off leash the owner is yelling at the dog to stay and get over here and they are acting hurried and excited rather than calm and confident. This causes the dog to become uneasy an run away. I don't think that people should let their dogs run free until they confident of their dog's recall willingness. When the dog backs away they shouldn't chase either, they should turn and go the other way.