Apps distributed for use on Android Auto have to follow driver-distraction-focused design rules on top of standard Play policy — no video playback, no manual text entry, and simplified interaction patterns suited to glancing rather than sustained attention while the car is in motion.
A common cause is a media or navigation app that ports its phone UI to the car screen without adapting it, keeping interactions (like free-text search) that Android Auto's review explicitly disallows while driving.
"Your app's Android Auto interface allows free-text input or video playback while the vehicle is in motion, which does not meet Android Auto's distraction requirements."