Think about it this way. Why would every single person disappear from the streets? It could be that a revolution happened. Everyone is locked in their houses, at risk of being beaten, tortured, killed, etc. Maybe it's a police officer, trying to enforce these rules? Maybe if it's some sort of city-wide issue, meeting people we don't trust isn't such a good idea, hm?
Maybe resources are scarce, maybe whatever is down there is a thief, trying to prolong his own life.
How about this: we will all carry a weapon of some sort, and beat him down when we see him, if we see him at all. Okay?