Automakers cant keep up with the phone makers. Apple and Android phone makers release a new phone every year, a new OS and new patches for the OS. Carplay and Android Auto of different versions may interact differently with cars that may be integrated to older versions of these software. Also except Tesla no other car manufacturer has successfully rolled out an over the air (OTA) update. Most cars the core computer updates happens at the dealer.
The second thing is the data. Auto makes dont want to give away the data to apple and android- because there is a great revenue potential for this data. For example today a number of insurance companies offer a dongle which monitors your driving and based on certain parameters you get a discount on your insurance premium. Once cars have connectivity (SIM card), the manufacture can then monitor this and sell this data to insurance companies instead of them investing in making dongles. Almost all manufactures have a connected vehicle technology group that is working on this.
Thirdly some of the premium car makers think that if they were to integrate Android or Apple and the software malfunctions then customers will say that the XYZ car is not working and not that the software of the phone is not working. They dont want this negative publicity (this has probably cooled over the years).
Other than apple and android, Samsung and Intel are working on the Tizen platform- which supports connected car use cases. Ford is working on OpenXC and urging other car makers to adopt this standard platform.
Over the next few years I expect car-phone integration to become an universal module with some basic feature and an open platform (like OpenXC) which allows developers to access car data and develop applications for cars and you can buy it from you car screen as you would on your phone or tablet.
One can only image how this will change with driver less cars- car makers may have to set up massive technology capability to make cars drive on their own- they are already doing this. One the entertainment side- imagine a scenario where you sit in your self driven Jaguar F Pace 2021 model and buy the latest movie from the InControl Appstore and watch it while your car drives you from one place to another