Even a cursory study of past predictions shows why not. On the whole, cultural predictions historically have been worse than random guesses.
Old books are a graveyard of prophesied futures that never came to pass.
A few prophecies hit the bullseye, but there is no way to discern beforehand the rare right one from the plentiful wrong ones. Since predictions are so often wrong, and since believing erroneous predictions is so tempting and so misleading, some professional futurists avoid predictions altogether on principle. They have a point. So few long-term predictions prove correct that statistically they are all wrong. Yet, by the same statistical measure, so many short term predictions are right, that all short-term predictions are right.