Consider the premise that the primary role of law enforcement is not to prevent crime, but to avoid vigilante justice. In that case, it is perfectly logical to

Consider the premise that the primary role of law enforcement is not to prevent crime, but to avoid vigilante justice. In that case, it is perfectly logical to ignore crimes with low probability of identifying the criminal and (relatively) low cost to the victim. If the perpetrator is exposed, it's now in the interest of law enforcement to step in and avoid a (potentially escalating) conflict between victim and perpetrator.