Since when has carplay failed?
Not that I agree with this assessment but developers interested in making their application work with CarPlay can't simply make the app. They have to contact Apple who approves of the process and only applications that play audio are accepted. Which is why there's no Waze application for CarPlay or Facebook Messenger or Yelp. Apple puts safety first, then privacy then security. They want applications that don't distract the driver and a lot of great applications that would work fine for the passenger to interact with or while you're parked aren't on CarPlay because of Apple's walled-garden.
There'd be WAY more CarPlay applications if Apple allowed developers to make them. Right now, the only 3rd party CarPlay apps I use are Overcast, Audible and Pandora. I'd love to see more.