Both airplanes and helicopters must be very, very reliable to be safe. They require lots of skill from their pilots, and frequent inspections and repairs from well-trained technicians. This means money. Also, there's noise to worry about, and all the debris blown up by the rotor's downdraft, and keeping people and animals clear of the spinning rotor. For these reasons and more, helicopters usually operate from carefully prepared sites, not from any old vacant lot or driveway.
People worry about traffic jams in the sky.
If tens of thousands or millions of aircars were sold, the present air-traffic control system would be inadequate to deal with them. A larger and fancier system would be necessary. Fortunately we seem to be quite safe from this particular threat. Nevertheless, for the heirs of Waldo Waterman, the dream of a versatile personal flying vehicle refuses to die. Wis. Among them, they've got dozens of designs for roadable aircraft.