I know its normal to get asked for license, registration, and proof of insurance. But why ask for the registration? When I register every year, the county sends me a sticker with the plate number and expiration date to stick on the lic plate. The cops van see the plate and date right? Plus I’m sure they run the plate when they pull you over anyway. Seems to me they already know the registration status.
So why do they still ask for the registration paper?
In California, proof of payment for a vehicle registration renewal is allowed as proof of registration, specifically to cover the period after the payment is sent but before the DMV has issued the registration and corresponding sticker. So even if the DMV hasn’t received the payment in the mail, if a motorist can show some sort of proof (eg a bill pay transaction on their phone), that is acceptable.
Also, the DMV here will issue one-day registrations, in order to allow a vehicle to be driven from one storage location to another. If a motorist has a proper one-day registration, that won’t necessarily show up on the police computer, but is nevertheless legit.
Both of those cases would only apply if the cop’s computer shows the vehicle as unregistered, hence why the cop would ask in those cases. It doesn’t explain why they ask for it every time, even when the vehicle is registered normally.
It’s also a chance for cops to look in the glove box, where most people keep their registration. Or to smoke out people who stole a car and thus don’t know precisely where the registration is.
But those are ancillary reasons for cops asking about registration. I figured OP only wanted the bona fide, entirely-defensible reasons.