Could the government set up 80,000 cameras to spy on everyone? No, they are not aloud to create dragnets or conduct mass surveillance. They need warrants.
Thats the loophole that flock capitalized on.
There is no expectation of privacy in public. Look at NYC, the government most certainly has setup a network of cameras without a warrant. Flock cameras are all (to my knowledge) in public as well
Reference: https://www.amnesty.org/en/latest/news/2021/06/scale-new-yor...
How many highways and bridges charge tolls via license plate reading cameras? A lot, it's legal, and I would be surprised if that data was used only for processing tolls.