Since cars do not have rights, nor do the plates, the reasoning is they are not violating your personal privacy. Courts and Police have so twisted the law as to deprive our rights by stripping our association with our property. Sadly they can simply initiate forfeiture against property still protected by the law.
There hasn't been sufficient push back to stop this erosion. Worse there isn't sufficient push back against government agencies holding back information which they are bound by law to surrender.
> Since cars do not have rights, nor do the plates, the reasoning is they are not violating your personal privacy.
Is that really the justification, though? The only justification I've heard is that you have no reasonable expectation of privacy when driving down a public road. It has nothing to do with you v. your property or the fact that your license plate does not have constitutional rights.
The courts have agreed that you can't mindlessly swap out a police officer for a computer, save all the data and keep going as you were, but that doesn't change the fact that you do not have any reasonable expectation of privacy in public.
It is interesting, that you mention forfeiture. In my opinion it is one of the biggest examples, how governments twist basic personal rights that are normally protected by the constitution.
Recently, I also learnt that even in the Magna Carta (1215 BC) the property of a "free person" was protected against the grasp of the potentate.
When modern governments now disable this basic right by legal trickery, than we in essence loose our freedom.