Car companies are NOT in the business of building infotainment systems. They are in the business of building cars. A while back, to compete and differentiate themselves, they all started to build their own touch screen systems with their own custom interfaces. All of them sucked. Even the ones that were the best of their class still sucked. Not only that, every single interface was different. Going from car-to-car meant re-learning a new system. They all have limited resources to throw at this problem so everything is sub-par. It's like going to McDonalds for good coffee -- no, you go to a coffee shop if you want good coffee. McDonalds just provides coffee because they have to. Same is true for car manufacturers.
Trusting the OEM is just a bad idea. It is better for everyone involved to give this responsibility to those who are good at it. Apple and Google both have huge ecosystems of accessories and application developers -- not to mention massive user bases. Apple and Google have entire teams dedicated to integrating with auto makers and ensuring that the experience is consistent across all vehicles.
So why would you want to pay thousands of dollars more to get, for example, a navigation experience on your car that sucks balls? Instead you can plug in your smartphone – which some have arguably more computing power than a lot of commodity PC's sold in the last few years – and have a vastly superior experience.