Unilateral hearing loss, or single sided deafness, is much more widespread than people realize, particularly in children. Because of this, the average person sees hearing loss as a black and white -- someone has normal hearing in both ears or reduced hearing on both sides, but that dismisses one particular kind of hearing loss entirely.
You may think it would be evident, but hearing loss will be gradual, so how does one know they have it? There's no shooting pain to function as a danger sign. You don't lose consciousness or make extra trips to the bathroom when it happens, either. It's safe to say the signs of hearing loss are more subtle than other autoimmune disorders like diabetes or cardiovascular disease.