I'd argue that we do try to write about the future, but the thing is: it's pretty damn hard to predict the future.
The problem is that if we look at history, we see it littered with disruptive technologies and events which veered us way off course from that mere extrapolation into something new.
I think you are entirely correct about the difficulty in predicting disruptive technologies. But there's an angle here I think you may not have considered: the possibility that just the cultural values and norms of the distant future might be so alien to us that readers wouldn't identify with future people or want to read about them and their problems.
Imagine a reader in 1940 reading a science fiction story which accurately predicted 2014. The idea that there would be women working who aren't just trolling for husbands would strike him as bizarre and not very credible. An openly transgendered character who wasn't immediately arrested or put into a mental hospital would be beyond belief.
Now send that story back another 100 years, to 1840. The idea that blacks should be treated equally and even supervise whites would be shocking. Go back to 1740. The irrelevance of the hereditary aristocracy would be difficult to accept. In 1640, the secularism of 2014 society and would be distasteful, and the relative lack of censorship would be seen as radical (Milton wouldn't publish his landmark essay Aereopagitica for another four years). Hop back to 1340. A society in which the majority of the population is not tied to the land would be viewed as chaos, positively diseased. But in seven years the BLack Death will arrive in Western Europe. Displaced serfs will wander the land, taking wage work for the first time in places where the find labor shortages. This is a shocking change that will resist all attempts at reversal.
This is all quite apart from the changes in values that have been forced upon us by scientific and technological advancement. The ethical issues discussed in a modern text on medical ethics would probably have frozen Edgar Allen Poe's blood.
I think it's just as hard to predict how the values and norms of society will change in five hundred years as it is to accurately predict future technology. My guess is that while we'd find things to admire in that future society, overall we would find it disturbing, possibly even evil according to our values. I say this not out of pessimism, but out my observation that we're historically parochial. We think implicitly like Karl Marx -- that there's a point where history comes to an end. Only we happen to think that point is *now*. Yes, we understand that our technology will change radically, but we assume our culture will not.