Instrumental and epistemic rationality tend to be correlated, because there is an objective world. Concepts are mental tools: don't ask if a belief is true, ask if it is useful.
Scientific theories are concepts, tools. The epistemic way to evaluate a scientific theory is to see how accurate its predictions are. This is epistemic rationality.
But the instrumental way to evaluate a theory is to see how adaptive believing it is. Is believing it good for your genetic fitness?
These are not the same. Science is a commitment to truth, but that is not necessarily good for you. Accurate predictions are not the same as utility.