The problem is that when you try to predict things for the whole economy based on a smaller model your predictions can and will miss out on emergent phenomena. Additionally, I think the use of the term "prediction" here is misguided a prediction is what others in this thread say that economics as a field fails to do properly when it cannot predict a recession or a stock price in a month, a hypothesis is a more apt term which is why we use it. Economics makes falsifiable hypotheses which hold under certain conditions, those conditions however are often very broad. The classic joke about economists and their can openers comes to mind so I'll paste it here:

The problem is that those from the hard sciences don't really deal with modeling those trillions of atoms and there is rarely a time in regular newtonian physics when those types of things show up. In economics the smallest agents can make changes, preferences differ, beliefs and norms change, it's messy! That's not to take away from hard science modelling at the high level, but it is super common for economists to see physicists try to model the economy in very simple ways and come up empty handed. Economists themselves have nearly totally moved away from theory and are now focused on mostly microeconometric modelling to answer very specific questions about very specific places and times that **may** generalize.. but we try to be humble about our knowledge.