Well, maybe they just can't cure this disease, since it's really a disease. I even had this and I still can't solve the problem with bad breath.
Yes, because the nerve endings responsible for the sense of smell are very quickly "overworked", so the nervous system stops responding to its own body odor, the brain simply ignores it. We begin to smell our own smell only in the event of any significant changes. For example: new perfume. Or the smell of sweat after sports. If the body has a permanent odor, even if unpleasant, the person does not feel it.
So, even you cannot say with certainty that an unpleasant smell does not come from you, even if you do not feel it.