I think most individual doctors are just ignorant of the science and the details of low carb eating. Also, they trust the medical establishment, which preaches low fat. I think individual doctors would change their minds if they had time to eduate themselves.

On the other hand, I think the medical establishment (and the FDA) have more of a stake in believing that we really NEED all those statins and other expensive prescription drugs and NEED to keep eating all the grain, corn, and potatoes the farmers are growing. And when you want to believe something, it is easy to make yourself believe it. So they keep putting out guidelines and statements criticising low carb.

Just my opinion.