They’re not a solution simply because they’re still cars, and therefore take up the same grossly excessive amount of space as non-autonomous cars do.
Yeah, the only things autonomous cars might reduce are:
Parking, but only if we forego our current private ownership model and everyone starts doing self-driving robo-taxis everywhere (unlikely)
Road fatalities, but only if the self-driving tech proves statistically better than human drivers in a wide range of conditions (jury is still out)
It's the same fundamental problem that electric cars have: geometry. Cars -- even if electric and self-driving -- are simply grossly inefficient at moving people for the amount of land they require:
