Besides Google's cultural issues, the fact remains that a whole car is difficult to build: heavily regulated, expensive components, very competitive established market. It is foolish for any company to enter making a new car when they could just sell their hot new tech into cars.
The feeling in the industry right now is that the car is the new cell phone: generally untapped and ready for rapid improvements and new service roll-outs. All the head units basically are Android devices now (to manage the tuner, the CD player, Bluetooth connectivity, the DVD player, GPS/maps, OTA updates, etc.).
Apple tried. Google tried. Samsung is about to try. And all of them learn sooner or later that these projects have 5-year ramps and 10 years of support, that the hardware is 10x costlier than they are used to, and that the OEMs and end-customers have zero tolerance for their "move fast, break shit" attitude. Completely difference business cultures. Honestly, the best way to make a buck is to partner with OEMs and sell a drop-in peripheral or service. Anything else will fail.