The average doctor knows next to nothing about supplementation.
Maybe. That's not been my experience.
Perhaps they don't know because supplements are hocus pocus. They are marketed with words like a new iPhone or a new car. If you doubt that Google any particular supplement and see all the outlandish claims that suddenly appear. There is no massive volume of evidence/research for their safety and efficacy. And that's what most doctors are trained on and follow. Most supplements are just words to convince you that they solve some problem you perceive you may have.