Trains and subways don't get you from anywhere to anywhere. They are incredibly expensive and take many years to add new lines, disrupting all kinds of things in the meantime. And they often take way longer to get you places. My time has value. There's a million things I'd rather be doing than waiting for a train, or waiting while a train makes tons of stops along the way that a car wouldn't.
And are you expecting me to carry bags of groceries on the train? How's that work? I sure hope the train has a stop in front of my house.
"With the tens of billions if not more spent on driverless cars you could have actually rebuilt a decent chunk of infrastructure."
According to this, it costs 3 billion a mile for subway. Maybe that's an extreme.... but still. You know how many miles of road there are that are currently used by cars?
https://sf.curbed.com/2018/6/18/17464616/bay-area-subway-tra...
Also, one nice thing about software compared to trains: once you've built the software, each additional copy costs nothing. And the vast majority of the self-driving car initiative is in developing the software.
Also, trains don't help with avoiding things like making grocery runs altogether. Self driving cars (and other robotics that are benefactors of the technology) can make it practical to eliminate the vast majority of grocery shopping and other typical errands, having a robotic system deliver it to your door more cheaply than going to an old-school grocery store.
As for your space analogy.... sorry, but this is just different. This deals with existing infrastructure, existing culture, and so on. We need a smooth transition.