http://uwb25d43nnzerbozmtviwn7unn7ku226tpsjyhy5n4st5cf3d4mtflqd.onion/posts/nophones/index.html
In short, they can quickly establish and almost in real time if people are deviating from their "normal" behavior. This gives some people enormous power, which is used whenever there is an opportunity to take advantage of that power (i.e. to surveil people). Technology is part of power, it comes from power and needs power.