A flying car can get you places faster.
An autonomous car allows you to sleep why getting there, effectively using time that you would have spent driving.
A flying car avoids congestion on the roads.
An autonomous car avoids congestion through superior knowledge of whats ahead.
There are problems that both approaches solve, in different ways.
A nice Apache gets you past the congestion in great fun and then can be used to clear a place to land. With features like that, autonomous is not that inviting.