You picked a bad example. You get any music/podcast/any-other-audio continuity with just Bluetooth. Likewise, you even get controls for music and audio metadata displayed.
What you don't (usually) get from car's regular infotainment:
- Maps that don't suck
- Maps that get updated often
- Navigation that is aware of more than just what HD Radio tells about highways
- Helpful notification when you get into the car that starts navigating to whatever is next on your calendar
- A choice between what navigation software to use
- Ability to switch between audio sources (i.e. go from audiobook to spotify)
IMO Android Auto and CarPlay generally implemented pretty poorly in pretty much anything, but Mazda.