It is really expensive to have satellites that can visually track a human. The Keyhole spy satellites are the size of Hubble (not coincidentally) and can resolv

It is really expensive to have satellites that can visually track a human. The Keyhole spy satellites are the size of Hubble (not coincidentally) and can resolve 3in. The much cheaper and smaller Planet Labs SkySat have resolution of 12in and could track a car. The issue is that would need constellation covering the whole Earth. That is doable, but not needed for observation so nobody has done it. Ships have an empty background and can be tracked intermittently while people and cars require continuous tracking. Drones would be better, but would still need a huge number to provide continuous tracking. CCTV cameras would be easiest but limited in area. Finally, tracking cell phones is doable, and easier to do with satellites.