There's never just one. Mainly political.

Those who in power of the state don't want to loose power. A protest, revolt is the best way to overthrow that. So to eliminate that threat is to survey. Install fear and you have control.

> The idea that emerged around the time of the French Revolution that the political spectrum can be divided into a right- and left wing in the first place – it becomes clear that the Left, in its essence, is a critique of bureaucracy, even if it’s one that has, again and again, been forced to accommodate itself in practice to the very bureaucratic structures and mindset it originally arose to oppose. [1]

[1] Computers and Surveillance Scandals in the 1960s-70s - https://sciencespo.hal.science/hal-03952774v1/document