A Google spokesperson explains:
Promoted pins in navigation are not new – they let people see relevant ads for businesses like gas stations, restaurants, and stores along their route. To avoid driver distraction, these ads do not pop up, expand only if they’re tapped on, and disappear quickly after a short time.
I like how they do the reverse psychology, at least for me. I have still the urge to press the non highlighted button, because in my time the “Buy”/“Go to play store” button was highlighted and this is just reversing this.