Although Google has started offering Waze on their Android Auto for some time, the version that was release was only the beta version and most of the people were not given access to Waze but that changed late last month when Google finally released the app on their Android Auto.
One of the reasons why some people would prefer Waze over Google Map is because Waze actually offers drivers real time information on what is happening on the road like accidents and also the weather up ahead so that drivers can be prepared for the journey.
If you would like to use Waze on your Android Auto make sure you have things like your phone address and more. Bare in mind that some features that exist on the phone app is not ready for the Android Auto yet but they are still working to make sure features like the speed limit will arrive in the near future.
Apple CarPlay users were hoping that the app could come to them as well but right now, it does not looks like it is going to happen.