I think a lot of patients/people don't know what a DO is because there aren't that many compared to MDs. There's roughly 140 MD schools and 29 DO schools (with a total of 33 in location).
Not to mention, most MD schools are associated with undergrad universities. Everyone has heard of Harvard, Yale, UNC, Penn State, U Miami, etc. These schools are known for undergrad, but also have medical schools.
DO schools don't have this (for the most part, with the exception of a few like MSU, Nova, Rowan, etc.). But why aren't universities like Harvard, Yale, etc. creating DO programs? They only have MD programs.
I think if DO programs expanded, and were affiliated with prestigous and/or popular schools, the word of osteopathic medicine will be spread, and more people will recognize DOs.