The official story is that they're looking for reported stolen cars or cars with stolen plates (although I can't see that given how fast they go through the lots, as they'd have to look at the vehicle associated with that plate), cars belonging to people who are being sought for some reason (warrant, felon, etc...), but the reality is the data is being collected on all plates. So, they can get an idea of who is where.
They build up data dossiers on people and then if you are not in your normal place if they stip you thry can asky why you arent doing x today, and are here instead?
I would imagine they are looking for people who didn’t renew their registrations.
Here in New York, we have window stickers, but many states have dropped them.
Believe what nutter conspiracy garbage you want, but its obvious that you have no clue as to how a plate reader system works.