If Google develop the car, they need to do all the end user support. This is not in the DNA of Google. If they provide the technology to a car manufacturer, they can extract a fair amount of money from them and they do not have to deal with direct end user support.
When my car has a problem, I want to talk directly with someone to get it fixed.
Google has ventured in that area though, just take a look at Pixel, their smartphone.
But the scale difference between developing a smartphone and a car is quite a big step. I am not that surprised though, getting into the car market is difficult and unsure. Just doing the technology part seems to make more sense imo.
Yes: and just take a look at how many people are unhappy with the support they get on their Pixel[1]. The number of people who would be able to tolerate Google's level of hands-off with a car, where the expectation is typically "for the first couple years if anything is even slightly weird you can drive it to your local dealer and someone's job is to try to make you super happy", is going to be much much much lower than the number of people who are currently tolerating it with consumer electronics.
I'd say the big difference here is running costs. I've worked with automotive clients (Ford, GM, Renault etc) for a while, and that's a big factor for them, especially in the lease market. Also given that a car is not a 'throw it away and hand the customer a reconditioned unit' item, repairs become far more expensive and time critical.
The sheer drag of maintaining a network of repairers, keeping them stocked with (Sometimes huge) spare parts, managing repair times etc is astonishing. I can see why Google and Apple would want to lean on established players instead of going it alone.
I would be excited to see acquisitions or serious partnerships from both Google and Apple. By partnerships, I expect something like what Google did with its Nexus devices. For example, a google car, manufactured by and advertised with Volvo, but with its own brand, logo, etc.
When my car has a problem, I want to talk directly with someone to get it fixed.