Probably the same reason Zoidberg is considered to be on the same level of medical competence as Dr. Dre (Zoidberg literally doesn't know human anatomy), and a higher one than Dr. Pepper (Which is genuinely responsible for less death than Zoidberg is), and Dr. Evil (Went to Evil Medical School)

And even then all of these people are probably better doctors than Doc, the dwarf who lived back in the days when washing your hands was considered a "Rookie mistake no self-respecting gentleman in the medical profession would ever make"

And the Medical Profession consisted of people wearing scary crow masks who just spread disease around and kill people, fully believing that disease was caused by not saying "Bless you" when someone sneezes