California's apparently special. I don't live there but it seems like...
A registration sticks to the car, just like the plates. It's someone's responsibility to keep it up. You have to declare it "in-op" to the DMV but this also costs money, just less of it, so some people don't think forward and stop paying entirely, because they hate their car/life.
If you sell a car, the buyer drives off in it with the same plates on it! You, the former owner, are on the hook until the buyer presents themselves for a new title. There's a form for that!
There are some other uptight states that require buyers to title cars within 30 days of buying them or fees start. The really anal ones want a safety inspection/ smog to pass this step as well, which is a hassle for that project hot rod.