The deciding factor in most things is cost. For example, it's all very well to design an automated car but it relies on an infrastructure. That infrastructure costs money. The way things are going round these parts, they aren't even repairing the road surface, due to lack of funding, let alone building in the necessary new equipment for autonomous cars to be commonplace.
Same with new medical research. The manufacturers can produce miracle drugs but they are often too expensive to be put in common use.
It's no different for airborne cars.
There remains the problem of customer resistance. If the customer won't buy the product, the designers have wasted their time.