As somebody who's had to deal with doctors because of a plethora of diseases, I must say you're absolutely right. (I also shadowed a few and am considering applying to med school.)

I don't remember what this concept is called, but basically it posits that "one should look for horses, not zebras" and is part of medical education. That is, a doctor should assume that the symptoms a patient has are caused by a common disease rather than by a rare one. So most doctors, thanks to their confirmation bias, dismiss any symptoms that don't fit the common disease diagnosis. (A girl from my town went to her physician because she complained of headaches. The good doctor said that she's got nothing to worry about and recommended more rest and relaxation. It turned out that the girl had a brain tumor which was discovered when she was autopsied. The good doctor is still practicing. Would this gross example of irrationality be tolerated in other professions? I think not.)

Most doctors are not so rational because of the way their education is structured: becoming a doctor isn't so much about reasoning but memorizing heaps of information ad verbatim. It appears that they are prone to spew curiosity-stoppers when confronted with diseases.