This has the smell of "Why don't I have a faster horse".
Why no flying cars. Because objects have mass and inertia and people are incredibly stupid. Making a flying car has been done. Making a flying car not be a weapon of mass destruction is very, very hard.
Because you don't fully understand your own point...
You look at science fiction and say "why didn't I get flying cars" and not "why didn't most science fiction predict a global always on network that put the furthest places away from you a few microseconds away from audio, video, or any other type of information that can be digitally encoded.
Trying to use flying cars as a gotcha is missing that flying cars aren't near as useful as one would think in relation to their costs. Moving information has become far more useful than moving objects long distances quickly, especially humans.
