Computers aren't reliable enough to fly the aircraft entirely on their own. Even if they were it would require a HUGE network of stacked and
redundant systems to handle the mass of air traffic. And even private pilots flying single-prop Piper Cubs have to meet the same FAA requirements as
professionals flying those "Mach 0.9 airliners".
Even flying low would create hazards for air traffic control. Approach vectors for major airports would have to be kept clear, and everything would
need to be confined to a very distinct airspace.
I'd like to see the battery that can handle that job. Hydrogen, maybe, but we can't even get the PTB to mass-market hydrogen-powered cars, and
hydrogen-powered aircraft haven't even been designed, let alone tested and approved yet.
But that mentality carries over into private aviation as well. Again, FAA requirements are just as stringent for private pilots and their small
aircraft as they are for commercial airliners, sometimes even more so. This leads to a conservative "if it ain't broke don't fix it"
mentality.
I don't think you really understand aircraft design and manufacture, or the regulation of such and the people who fly them.
Right now the technology simply does not exist to make a car that can drive on the ground and also fly, and do both with equal levels of safety,
reliability and efficiency--and make no mistake, cars will never be totally free of the ground; you wouldn't want flying vehicles traveling in
congested urban areas at near-street-level.
We're talking totally new propulsion systems, cutting-edge materials, high-powered fly-by-wire computers, advanced servomotor systems, whole new
integrated navigation systems, new safety systems, new fuels, totally new infrastructure to handle the traffic, and an entirely new set of laws and
regulations to govern the whole thing.
The vast expenditure to do all of this, and the time it would require, far outweigh the cost in money and man-hours, and the sheer utility, of
expanding mass-transit systems, improving traffic control for cars on the ground, and moving cars away from gasoline and diesel using technology that
is tried and proven and sitting on the shelf right now just waiting for the funding to put it to use.
Shifting to flying cars is reinventing not only the wheel, but the whole of society. Such a change in the current political and economic climate, and
the climate for the forseeable future, is highly unlikely.