I think there might be an issue with different branches of law enforcement and government having different remits and priorities.
The average policeman doesn't really care that much about illegal street vendors. His main job, outside of reading the newspaper and smoking Double Happiness, is to catch the bad guys.
Traffic police buy fancy sunglasses, keep their gloves whiter than white and enforce a One Scooter, 2 People Forbidden Policy.
The beloved Chengguan confiscate fried potatoes, outdoor seating and the like.
The list goes on.....
Until all branches work together, recognizing an infringement and reporting it to the relevant department involved whilst staying on scene to supervise until help arrives, the general populace must find it hard to place their trust in their gov't services and law enforcement.
It seems faintly ridiculous that if, after a traffic accident, the two (or more) protagonists end up in a physical confrontation, the traffic police stand idly by, completing their traffic report, utterly disinterested in any violence that falls outside their traffic remit.
Years ago I had a car crash in central London and as it happened the first police on the scene was a fully-armed, body armoured SWAT team who were two cars back. They sorted out the accident as best they could and waited until local police turned up to take statements, breath tests etc... It was re-assuring to be surrounded by 6 heavily armed men in the dangerous reaches of the King's Road in Chelsea!
In China, taking on more responsibility than you have been assigned is anathema. There is no upside for a policeman who jumps in to help out on someone else's turf. If anything goes wrong the offending policeman will have all blame heaped on him.
So, the policeman will happily buy fried potatoes and will do so right up until the moment the potato vendor breaks a law that his unit cares about.