I'm pretty sure that once you outfitted a Cessna with the sensors to bring it up to drone levels of capability it's not going to be cheaper anymore. It'll certainly have several times the fuel operating cost simply because it's considerably heavier, and lack the loiter time and covert nature of a drone. (Hint, this has been done in various South American countries, the drones are better.)
The article is also hilariously alarmist. So they track a car for training purposes; it's cheaper than the article's proposed alternative, and it's completely harmless since they're not targeted and they're not running a ****ing license plate or something and they're not calling the cops on you if you're speeding.
And even if they were, this wouldn't be very different from existing police helicopters, which is what makes it dumb like the privacy argument against stoplight cameras is dumb; you're out driving around in public, anyone can see your car, you have no reasonable expectation of privacy unless or until somebody tries to open the trunk or look under the seats.