It's voice-operated. Look at a CarPlay video - clearly usability was not given too much thought there, and it requires plenty of physical button presses to operate.
The interface manages to pack a lot more information yet manages to be more readable because it's not using an illegible typeface.
CarPlay is extremely basic. It's a frontend for a couple of apps and that's it. Android Auto gives you tons of information and is extremely integrated.
Not to mention, the API is opened to ALL DEVELOPERS.