The world has been brainwashed through history that the only people who are true doctors are M.D.'s, thereby disenfranchising via word alone all those others who have also done doctoral work: DO's, OD's, PhD's, ND's, EdD's, chiropractors, ScD's, etc. When someone says doctor, people naturally think "medical doctor," hence M.D.
But, in my opinion, DO's are also responsible for their own obscurity through their behavior of hiding their credentials and avoiding explaining that DO's are medical doctors, too. At my doctor's office and in the surgery wards, all the DO's wear lab coats or scrubs that say "Dr. _____" while all the MD's wear lab coats that say "____ M.D." Why not say "____ DO"? I recently saw book by "Dr. Tom Yee", a DO, while all the other medical books written by MD's say things like "_____ M.D." Why? I saw a newspaper ad for a DO plastic surgeon. Dressed in scrubs, smiling, but no where on the ad does it say DO except in small print. His scrubs say "Dr. Craig ____." Why doesn't it say, "Craig ___ DO"
As long as DO's hide their credentials the rest of the world is never going to know what DO's are and what they can do vis-a-vis MD.s Training more DO's helps, but DO's need to stop hiding who they really are from the public, who are the ones to disseminate what DO's are like.