Interestingly, in the UK it’s just surgeons who deliberately don’t take the Doctor title.
The history of this difference is that surgery used to be the domain of the barber-surgeons who had their own training separate from medical degrees (in the era before anaesthesia and antiseptic, being fast and keeping the patient alive were key skills here), so modern surgeons don’t go by “Doctor” in reference to these origins of their specialism.
