Most of this ALPR data is stored in databases for extended periods of time—often as long as five years. The databases may be maintained by the police departments, but often they are maintained by private companies such as Vigilant Solutions or Flock Safety. Law enforcement agencies without their own ALPR systems can access data collected by other law enforcement agencies through regional sharing systems and networks operated by these private companies. Several companies operate independent, non-law enforcement ALPR databases, contracting with drivers to put cameras on private vehicles to collect the information. These data are then sold to companies like insurers, but law enforcement can also purchase access to this commercial data on a subscription basis.
The government does not own the database, nor is this a California wide thing. This is local police departments being permitted to use private companies to maintain databases of citizen activity, and those private companies have developed a robust system to share that information.
Remembering of course that these cameras are mounted on public infrastructure. People are paying taxes, and that tax money is being used to buy, mount, and maintain these camera systems, but the actual data is not in a database the government of California (and by extension the citizens of California) has direct control over.
It would actually be better if the state of California had its own database because it would be more scrutinized than these random private databases that cops are allowed to put together and host on some private companies server.