Why do car registrations say "non-transferrable"

meaning you have to have the title with you, when you go to the DMV to switch the registration over to the person you’re giving the car to? (I guess if it says “transferrable” you can just sign the back and that’s it?)

In my state, you can’t be registered without proof of insurance. If you could transfer registration, it would be possible for the new owner to skirt that law, at least for the remaining duration on the registration.

You can’t transfer registrations, period, with or without the title. At least not in my state. The new owner must apply for registration independently, on proof they are both the owner (legal holder of the title) and insured, and a few other things besides.

New York State registration:

more reading! well, I’ll get to it, thank you. I think I know where the title to the car is, that’s something.

Don’t forget that unless it’s a transfer between immediate family members, you may have to pay sales tax on the NADA value of the car, even if you’re “officially” selling it for $1. Check with the DMV.