Do the sorts of diseases ML is being used to detect have a flat incidence profile over age? Even if they do, negating other diagnoses that are age dependent would still mean ML models would acquire a measure of patient age, say.
Almost every noncommunicable disease of adulthood becomes more common with age. (The diagnoses in this paper were things like "cardiomegaly" which are mostly just X-ray findings and, while they have ICD codes, are not a meaningful diagnosis that a practicing physician would care about.)