If you continue the argument that surveillance used to proactively rather than reactively find evidence is not a search, then with technology as it is today functionally there can be no expectation of privacy in public (somewhat fair) nor in private, given how widely distributed technology is - one could easily argue that technology's wide distribution is in part because of an expectation of privacy.

There must be a line for which people can expect privacy, or else privacy cannot exist. Its a fundamental value of liberty.

This isn't a case where they've identified a suspect using some specific investigative lead, reasonable suspicion, or probable cause.

Instead, they're using a widespread fishing tactic - a "dragnet" - to gather information in order to generate suspects without any reasonable suspicion. This kind of behavior has been found illegal in the past, because it clearly violates constitutional protections.

Using it to fish for other violations is where it crosses into the fuzzy and sometimes outright illegal

The counter to this is demand that they write you the ticket for the moving violation, don't answer any questions other than providing the legally required license, registration, and insurance, and move on

If they don't have evidence of a crime, they can't detain you forever on the roadside

Nope. You need not stop everyone -or even anyone!- you search for it to be a dragnet search.

A search that is widespread and indiscriminate is a dragnet search... regardless of whether it's done by agents of the government or by the private sector. [0]

The thing being caught in the dragnet is not people, but information about with whom those people caught in the dragnet associate, where they spend their time, and other details about their private lives that -frankly- the government has no business knowing without either paying the cost to have a police follow those surveilled around, or justifying beginning and continuing the search of specific individuals to a court and receiving its approval.

[0] I'd love for the courts to start generally taking notice of the fact that a private sector company for whom the overwhelming majority of its customers are public-sector law enforcement is very likely to be defacto acting as an agent of the state. Private companies acting as agents of the state have far more strict regulations that apply to them, and it'd be really good for courts to catch up with the current situation on the ground regarding the public sector's "partnerships" with private-sector companies like Flock, Axon, and similar.