Because they weren't willing to use the amount of oppression and violence necessary to subject the population to their control. That's a good thing but it makes

Because they weren't willing to use the amount of oppression and violence necessary to subject the population to their control. That's a good thing but it makes an occupation much more expensive. But imagine what would happen if they did any of the things I said like mass surveillance. The US is certainly moving in that direction, but imagine when there are microphones and cameras everywhere, always recording. With AI good enough to automatically figure out who you are and what you are doing. When every face and license plate is recognized, and drones above track where every single person and vehicle moves.