> I don't understand why a police cruiser can sit in a public space (or even a private one) and write down licence plates and descriptions of passers-by with pen and paper, or record everything around them with dashcams and bodycams for later use, but when it comes to cameras on a pole this would require a warrant.

Similar issue: cell phone interception via Stinger cell base stations by law enforcement. A U.S. judge in Ohio ruled that using the device to sweep up data from thousands of unsuspecting individuals to track one suspect gave the government unconstitutional, "unbridled discretion" to monitor private citizens.

Another similar issue: A judge in Mississippi ruled "tower-dump warrants", where law enforcement requests info from cell companies on users/phone numbers in a geographic area in a certain time frame are illegal and too broad. The judge declared them an arbitrary government intrusion that violates the Fourth Amendment's particularity requirement

A third similar issue: In U.S. v. Chatrie, the U.S. Supreme Court ruled 6-3 that reverse-location "geofence warrants" constitute a Fourth Amendment search. The ruling establishes that users maintain a reasonable expectation of privacy over their location data, meaning law enforcement can no longer execute warrantless, sweeping digital dragnets through third-party data.

These are 3 examples of large scale police surveillance that have been ruled illegal because they are broad surveillance and give police too much power without a specific legal justification. This seems very similar and I expect the court cases on ALPR cameras to end up in the same place, but it may take a decade or so.