I'll get right to it. There are two things that tend to be the genesis for future oriented science fiction*; an extrapolation of current trends, or an exploration of a possible future technology. The problem comes from the fact that trends and technologies don't develop in a vacuum. While someone is hard at work making artificial intelligence happen, someone else is hard at work making biotechnology push new boundaries, and a third person is ensuring that nanotechnologies** will do something more practical than making things slippery.
So if a science fiction story tells us that there are flying cars, the author better have extrapolated out the how and why of it to everything else in the world. Flying cars mean that there's a propulsion system that can lift relatively heavy things and move them with relatively high precision. It would have to be at levels of efficiency that rival wheel based transportation. This means that it can't just be a new fuel system, because a car with wheels will always be more efficient than one that flies. So either the fuel requirements are reduced to the level that people just don't care about the increased costs, or some technology is developed that brings flying car costs down to the level of cars with wheels while not reducing the cost of cars with wheels.
So in a world with flying cars, do we see desks that float in mid-air? If someone moves a hospital bed, it shouldn't be on wheels either. In fact, there should be flying buildings that utilize the same technology as a way to stay disaster proof and increase mobility. And since this technology presumably runs on some sort of anti-gravity technology (one of the only ways to make it worthwhile without dirt cheap energy), we should see weapons based on it, as well as space travel. And if dirt cheap energy is the reason we have flying cars, then we should see vast changes in the social and cultural landscape.
The problem is, people (authors) just don't think things out enough. A lot of science fiction has things added in that aren't explained just because it looks cool. While that's a fine endeavor, I'm much more concerned with the future and what it holds.
I would guess that the reason I notice this so much is that I read a lot of old science fiction. Asimov and Heinlein are particularly bad about this. Even as the technology progressed in the real world, Asimov's worlds never real progressed past the state of the art of the 50's. Heinlein's Stranger in a Strange Land had robocabs but no speech-to-text. The mail is physical, coming in envelopes. I firmly believe that someone writing in the 60's could have predicted the internet and everything it came with. Pretty much the only thing the internet did was make communication free. With that came a few silent economic and social revolutions.
Good sci-fi is based off of good science. Making a believable world is as easy as looking at the modern one and figuring out how everything will progress in the coming years.
* This as opposed to present oriented sci-fi, in which aliens or the like decide to visit Earth.
** Ten years from now, blogger won't highlight nanotechnology as an incorrect spelling.