It's a protocol designed to access certain mobile functions from the car's systems (and receive video output to display) that is designed to work with devices by Apple only, ie locking them down to only using one device.
Why would a manufacturer want to implement a feature that only some customers will want to use, pay Apple for the privilege, while (apparently) engaged in trying to create an open standard to achieve the same thing that ANY device and ANY car will be allowed to implement, for free?
Maybe they will implement it as an option in the future and pass on the Apple licensing fee in the cost for it. I certainly would be put off buying any car that forced me to pay for a feature I couldn't & didn't want to use.
Or maybe when there's an open standard for something similar they will implement that instead, allowing people with any device to use it.
This is just like the Siri Eyes-free proprietary nonsense to be honest... big fanfare about it when it was announced, bit of a flop since then. Have you ever seen a car with it? I haven't, not even in the options lists. I guess everyone decided it was stupid to put a bit of tech in a car that requires hardware from a single manufacturer to use...