Shopping is the main one. Cars allow shops to be very large (providing more variety and creating economies of scale), and the ability to site shops in cheaper locations contributes to lower purchase prices.
The other classic problem with public transport is that it cannot replace the point-to-point nature of cars. Sometimes that matters, sometimes it doesn't. But it matters for enough people that cars are the dominant mode of transport.
Self-driving cars will help some of this, particularly the car daycare problem. Though they will have problems of their own. Ever tried to get a taxi at rush hour? Ever been on a bus with suspiciously damp seats? People will still want their own cars and will still want to travel at the same times.
As an aside, one thing I really like about my city (Perth) is that there are a number of free bus routes in the CBD. You really do find CEOs riding the bus to get around.
Let me put it in networking terms.
Cars provide a circuit model. You go from point to point over a single dedicated "channel".
Any kind and combination of public transport does not do that. It is a packet model and you, the human, are the packet. You must change modes of transport and hope that they sync up, aren't running early or late, fit your schedule and so on.
Except in the cases where point-to-point travel takes substantially longer (very dense urban cores), I think most people will always prefer cars.
(Yes, I know the analogy is imperfect because the car can be seen as a packet blah blah blah. But cars are not sentient. Humans are and it is humans who decide what mode of transport to use.)
As a society we seem to have mostly established the abstraction that energy is free and unlimited. From the recent explosion of amount of things humanity does we can see clearly how practically free energy is a desired state. However, we're not there yet. Until we really get there, forgetting that this is only a leaky abstraction is dangerous, as the leaks have deadly consequences.
None of that matters. Who decides which transport to use? Humans. What measurement do they use? It's clearly not litres of diesel per passenger-kilometre.
"Humanity" is pretty good at economising scarce resources. But people are pretty clearly prepared to pay enormous costs (fuel, parking space, commute time) to have a private car. Arguing with revealed preferences doesn't change them.
What they do have is lots is support for shopping and public transport including wrapping packages so they are easier to carry (buying a printer they wrap a secure handle around the package to make it easy to carry home) and most stores offer relatively cheap and convenient delivery.
I am especially bullish on that delivery service. Sure, they use a car, but one small truck making the rounds seems a lot more efficient than lots of small cars driving to the store.
Shopping is a very trite activity, owning a car doesn't make it much better. In fact driving out to some shopping center seems to make shopping a day trip, which is one wasted day. I prefer to just pick up a few things on may way home from the tube, and ordering more complicated stuff from Amazon (plus the weekly food deliveries).
I live in Boston, and I'm fairly certain that the local Porsche dealership is catering to potential customers with very early morning test drives on Storrow Drive with demo cars. During the summer months I almost lose count of the number of 911s I encounter at 2AM (with a driver and a passenger, almost always both male) with window stickers on them, carving through the elevation changes and off-camber corners well beyond the speed limit. Last year it was so frequent I just got over to the rightmost lane whenever I would hear a wailing flat-six approaching.
The summary is that the commutes are brutal, but the private cars get to work and get parked, off the road, and they're not a big deal. But cabs are on the road and take up space all the time. The 2,000 additional cabs will cause traffic to move 12% slower, including deliveries, buses, and commutes.
People commuting in/out of the city is not as bad as just getting around the city.
http://www.npr.org/blogs/money/2012/07/31/157477611/does-new...
http://cityroom.blogs.nytimes.com/2008/04/07/congestion-pric...