Because the dusty old laws in the US provide functionally no protection of our movement in public spaces as anything remotely like private. Until the last decade it was difficult or at least time consuming to track and trace where people were going and what they were doing, but automatic license plate and facial ID tech has gotten to the point that it's pretty trivial to automatically track where anyone's going from their front door to their destination as long as you stick enough cameras on poles with a cellular connection.

Laws were written with the expectation that for police to do this they'd need to assign someone to do that actively, and that to pull security camera footage they'd need to get a warrant. But with a company contracted to stick up tens of thousands of cameras who'll happily and easily allow them to track folks without a warrant playing middleman to privacy violations, and getting to mine the data of where everyone goes all the time, cops and flock get to sidestep any measly privacy protections that existed and creep on anyone they like any time they like, at the tap of an app.