This is more of a ex-British empire thing, but at least some surgeons I have heard of in Australia insist, among medical company, of being called "Mister" not "Doctor", to set them apart from "mere doctors".
I think this is a formal distinction in the UK, but in Australia I think both groups can be called Dr.
It is also to do with the doctor-patient relationship. The surgeon-patient relationship is far more limited. A patient is refered to a surgeon by a doctor for a specific treatment.
I think this is a formal distinction in the UK, but in Australia I think both groups can be called Dr.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1119265/