Because it’s just a guess?

… Why Is It So Hard to Predict the Future? - The Atlantic.

The pattern is by now familiar. In the 30 years since Ehrlich sent Simon a check, the track record of expert forecasters—in science, in economics, in politics—is as dismal as ever. In business, esteemed (and lavishly compensated) forecasters routinely are wildly wrong in their predictions of everything from the next stock-market correction to the next housing boom. Reliable insight into the future is possible, however. It just requires a style of thinking that’s uncommon among experts who are certain that their deep knowledge has granted them a special grasp of what is to come.