So exactly what do you say to suspicious bike thief man? Do you say "excuse me, is that your bike?" what does suspicious bike thief man say? "yup. Lock's broken." I mean, it's not there's any convenient way to prove ownership of a bike. You can't run the tags or ask for the license.
I'm completely unsurprised that no one said anything. I get the impression we're supposed to be appalled. It doesn't seem like a situation anyone can really do anything about. I thought the point of bike locks was to make it too inconvenient to be worth stealing.