This is the thing I hate most about dealing with doctors. As a child doctors failed to diagnose in me a condition so obvious that a friend of my mother, who works at an airport, was able to figure it out from a mere description. Still my mother had to get angry with the doctor before he would perform a simple blood test for it!
Like in any profession, most of them suck at their job. That wouldn't be such a big deal except that the system in the US is set up to make it absurdly difficult and ludicrously expensive to shop around.