That may be ab implementation detail of android auto for your car manufacturer. I never needed to sync the contacts in BMW and VW.

I had some troubles with Ford, but there It worked via USB instead of Bluetooth pairing without forced sync.

Edit: I am in Germany, so data protection laws may also be a reason why it works for me

Android auto provides notification content to the car. Also of course a virtual screen.

So, there is not much that may be an issue. And you don’t habe to share your contact data with your car if you want to do hands free calls. That’s a plus