To be altogether trite: Technology is playing an increasingly large role in our lives, a lot of it seemigly ripped from science fiction tales of yesteryear....
In other words, these elements are no longer fantasies we can escape into. They're the world we live.
Alternately, a lot of fantasy deals with wish fufilment based on stuff that will always be impossible (magic) and a sizeable amount also leans towards worlds which operate either on magical principles or pre-industrial principles, or places otherwise alien to our humdrum existence. Fantasy's escapism then isn't something the next technological development can catch up with...
I've been mulling this. SF is pseudorealistic, and people in this time hate reality, therefore hate pseudoreality too. Well, this seems to be another Counter-Enlightenment-lite explanation of the relative popularity of SF vs. fantasy.
However, most popular literature tends to be in some degree escapist. Some of the older SF tropes have been around long enough to be regarded as mere conventions, no more to be viewed critically than, say, the faux mediaeval social structure in most fantasies or the neo-Victorian empires of most steam punk. The question, as in my ignored example of SF romance novelists vs. fantasy romance novelists, is why real viewers can easily tell the difference? And, why they don't like the SF? Personally, I'm rather inclined to see more than just familiarity breeding contempt but an deeper commitment to irrationalism flowing from perceptions of the trend of the (social/political/economic) world.
The SF=fantasy proponents however have been arguing that 1) there is no point at all to the pseudorealism of SF, that it serves only as a story device to facilitate willing suspension of disbelief and 2) that SF is manifestly just as unbelievable as any fantasy. Formally this is completely contradictory, except their tacit presumption is that they
are too superior to the SF fan to be taken in by such guff.
Yet this doesn't answer the question, why do fantasy fans, the large majority now, find it quite so easy to distinguish SF and fantasy modes, even in genres they like, such as romance? This fact gives the lie to the self-flattering assumption that hoi polloi are unable to distinguish SF's threadbare invitations to willing suspension of disbelief from the blatant appeal to the delight in the impossible and irrational in fantasy, instead seeing escape in both.
The hopelessly confused/deceptive chatter about plausibility seems to be the primary factor obscuring views here. The diversion into Avatar is a prime example. First, dragons in fantasy have been changed to suit images from paleontology of pterodactyls and pteranodons. The "dragons" in Avatar are not just a fantasy trope, not even on a literary lord's say so.
Second, the biggest implausibility in Avatar, bigger even than ignoring the effects of the suppose magnetic fields that hold up the floating rocks, bigger even than the breasts, is the body telepresence machinery. The information needed to carry all the sensory data to the human brain in the bed cannot be transmitted when the movie simultaneously depends on the impossibility of simple voice communications! But, if the machinery is supposed to copy the mind, then the avatars will never be unconcoscious. Not only is this tech implausibile, it is impossible in the context of the story. Except of course we "see" it work.
Third, as stated, the God that works is in fact plainly supposed to be natural in origin. I suppose it is possible that the sequel will reveal the natural origin to be due to the blue guys' command of natural science. We should then see Avatar pretty much as the first movie commentary on transhumanism and sustainable immortality, a kind of hard SF. But the real issue in Avatar is whether the movie would have been the same if Eywa had just turned out to exist, on grounds that another world must have different rules and magic like Gods is just as "plausible" as any gobbledygook about trillions of neurons. Would Avatar have been just the same? I think the answer should be intuitively obvious: Hell, no!