Its not necessarily that the function depends on something 'very unpure', its if it depends on anything which is non-primitive that is created or assigned within the component fn body.
window.location returns a Location object which is not a primitive, and so it will trigger exhaustive deps if it is being used by way of a reference inside the component render function (assigned to a variable), since it could theoretically be a different object reference on subsequent renders.
Since the linter can't necessarily tell if the reference has changed out from under it on subsequent renders due to the fact that it could be mutably changed, it marks it as a necessary dep.
window.location returns a Location object which is not a primitive, and so it will trigger exhaustive deps if it is being used by way of a reference inside the component render function (assigned to a variable), since it could theoretically be a different object reference on subsequent renders.
Since the linter can't necessarily tell if the reference has changed out from under it on subsequent renders due to the fact that it could be mutably changed, it marks it as a necessary dep.