Not everyone wants to ride in a bus. In fact, in my country people are stopping using buses, and doing some kind of car sharing, because it's much more convenient (available when you need it), they charge the same, and even though it's not much better space wise, a lot of people prefer riding with 3 others, than 20 others. This has been a growing trend, and I think it's inevitable that it will happen everywhere in the world.

Also, this is exactly the kind of service self-driving cars would offer in the future.