GM right now is the most vertically integrated of all the companies making meaningful progress on Robotaxis. They have a dedicated assembly line set up building off the Chevy Bolt platform, and intend to have 'thousands' of them on the road before the end of 2018. They're building their own ride hailing app, called Cruise anywhere, currently only available to GM employees. They've got On-star, which provides in-house expertise with connected car and vehicle diagnostic services. GM's Maven subsidiary offers car sharing services.
But when Robotaxis really proliferate fleet management infrastructure will be very important. Apple and Waymo have made partnered with Hertz and Avis respectively, but General Motors can utilize the real estate and expertise of it's existing network of dealerships, which can save them from a great deal of capital investment as Robotaxis dissemintate.
Before last December there wasn't a whole lot to be known about Cruise's progress, but since then it's just been one reason after another to be getting excited about what they're doing.
I was involved in a project at a major US auto maker where they wanted to utilize spare capacity at the dealers on something similar to what you are discussing. In this case, we would pay the dealers to utilize that capacity.
In some states, the dealer networks are large, politically very influential, and are not inclined to allow anything that will disrupt the status quo of selling and leasing cars. They absolutely had their hands around the throat of the auto maker and forced us to go another route just because they saw what we were trying to do could possibly change their income flow in some small way.
In theory, GM has the infrastructure and is making the right acquisitions. In practice the vast majority of the company is entrenched in selling and leasing cars and many people in the company don't have the imagination to see the world differently. GM has a lot of internal and external politics to overcome before they are successful with autonomous cars and Robotaxis.
Generally you tend to have to go 150-200mi to get to a different parent company.
I still think Seattle is more difficult to drive in. The streets are narrower (most residential streets are two way, but only wide enough for one car width, requiring drivers to negotiate with other drivers on how to proceed). There are far more 3,5,6 and even 7 way intersections. Just as many hills as San Francisco, but the several poorly-intersecting street grids give the hills much worse visibility. And I'm willing to bet we have way more construction than San Francisco.
I think it has more to do with them not having a snowball's chance in hell in Boston, Rome or New Delhi (in increasing order of difficulty).
We haven't even seen a driver-less car floor it on a green to make a left before the opposing traffic moves.
Of course, this isn't an issue in San Francisco, because the intersection is completely gridlocked. The only way you're going to make a left turn -- or even a right turn at many intersections at rush hour -- is by violating various traffic laws up to and including the Pauli exclusion principle.
I can't imagine how to build a self-driving car that can perform both safely and effectively in any major urban environment... and I'm not the type of person who says "I can't imagine" lightly. It would literally be easier to work on autonomous rockets at SpaceX. With self-driving cars, the engineering problems are largely social, not technical.
That said I remember the occasional drive straight down a cliff in Pittsburgh beating even the SF hills.
Unprotected left turns are one of major ways pedestrians are murdered by careless drivers.
Of course, the manufacturer can say "we will give you $x off your car purchase if you let us use your lot" but the reality is the dealership can just tell them to take a hike.
Also, manufacturers lease to rental car companies. So that is an option as well. I can imagine Enterprise having unrented cars in a lot that switch to robotaxis...