Now and then, including some plain falsehood may help, as when maps make the roads seem much wider on the map than they are in reality. A map has to have a lot of truth in it. A map that would show Philadelphia in the west and Pittsburgh in the east would not represent Pennsylvania as it is, and at best could cause confusion and make the map useless. But, on the other hand, no map is perfectly accurate. Maps are designed to be useful, not to be true.
Macroeconomic models are that sort of models.
Complex as they are, they are radically more simple than the national economy they represent. They leave out many details that could be important for other purposes. They are designed to help us find out way around the macroeconomy and understand how it changes and where it might go next. It distorts a few things in the hope of making the important things more clear.