Finally there are a number of people who are nervous of dogs, yes even your well trained friendly wouldn't hurt a fly dog. So the last thing they want is to be confronted by a dog off a lead, when they have no idea whether you are the best or the worse dog owner in the world.
Me for one. I absolutely love dogs but having been mauled by one years ago , it ripped at my arm, a Labrador as well. It was tied up outside Tescos at the time. I am so nervous of them. I have made friends with a Japanese Akita who lives locally and she and I get on like a house on fire. I honestly think she is more nervous than me. She stands behind her owner if anyone comes along.