This is true in physics where the system being modelled is governed by stable laws. You can confirm the model's predictive usefulness by experiment. If you test the model and find its limitations, you expect them to hold in 50 years' time.
Economic models, however, are themselves part of the economy. The ideas they are built on and their predictions become part of wider knowledge and influence the very thing the model is trying to predict or explain, possibly reinforcing or weakening certain behaviours. If a simplified model becomes widespread it can lead to blind spots in our understanding which cause systemic issues.
Of course that doesn't mean the model was bad or unsuitable for its original intent. But a simplified model can, in the wrong hands, be a net negative.