Because it looks to me like the stock market has a tendency to follow an exponential curve - or at least a high degree polynomial. I also believe that to a certain extent the stock market is bound to the real world and in the real world growth is currently not following an exponential/high degree polynomial curve. The tension between the two is causing an oscillation to develop which overrides the tendency for high disorder in price movements.

In short I think that over long time periods stock markets show some degree of predictability. They are not perfectly disordered because the they are bound to systems operating in the real physical world which display predictable behaviour.