Incredible huh, it's also due to the acceleration of technology. If you wanted to do this in, say the 1970's, you'd have to hire someone to follow each car. With video cameras with good enough resolution you can start recording things, but someone would still have to watch them, or review the recordings manually. Now, computers can read licence plates and recognizes individuals from their faces, they can have eyes (cameras) everywhere and they don't need sleep. And Petabytes of storage are affordable.

Was it DHS that had drones constantly recording Cleveland from the air, and if something happens they can just rewind the footage to see who, where they came from, etc? (Also being used in warzones, IIRC)