My take on this is, economy depends on human decisions whereas "pure" physics does not. To predict stock values even for one major company, with the greatest possible certainty you'd have to take into account everything that goes through the minds of the entire world population. And even that wouldn't be 100% precise because there would be unexpected events, such as natural disasters, probably even harder to predict than human decisions.
For some reason the theoretical economics is, instead, trying hard to ignore the human factor and squeeze patterns out of what's happening in the economy, i.e. the system is viewed pretty much like an isolated thermodynamic one. From this perspective a human being is merely an automaton that buys and sells stuff, just like molecules in thermodynamics are just little thingies with a few simple physical properties. Except humans are obviously far more complicated than that!
For some reason the theoretical economics is, instead, trying hard to ignore the human factor and squeeze patterns out of what's happening in the economy, i.e. the system is viewed pretty much like an isolated thermodynamic one. From this perspective a human being is merely an automaton that buys and sells stuff, just like molecules in thermodynamics are just little thingies with a few simple physical properties. Except humans are obviously far more complicated than that!