Another advantage of the "it's on your phone" aspect is that it follows you when you switch cars. If I use my friend's car, I still have MY system. If I rent a car for a trip, I still have MY system.
Another advantage of the "it's on your phone" aspect is Consistency. You get into a new car, all you need to figure out is how to open CarPlay, no need to learning a completely different and often complicated infotainment system.
For people who use car share services, this is a godsend. It feels like every other trip we take is in a new vehicle we've never used before, but all we have to do is plug the phone in (which we would do to charge anyway) and when we bring up maps to check the route to my in-laws' place it already has the address saved, my playlists available, etc.