I always assumed that physicians were commonly called doctors because they were the most commonly encountered higher-degree holders in most people’s experience. (Especially in pre-modern and medieval society where few people outside of clergy were univeristy-educated.) But of course, the basic medical degree in the UK is a bachelor’s degree, not a doctorate.
I know that the American MD and the British MBBS are entirely equivalent and the difference in terminology is merely accidental. I also know that neither degree is the same as a PhD, which some people hold as the benchmark for a “real” doctorate.
At least in the US it makes sense - the set of people addressed as “Doctor” is nearly identical with the set of people holding degrees that end in “D.” Why is it different in the UK? Why isn’t the medical degree called a doctorate if its holders get to be called “Doctor”? (Or vice versa, why are they called “Doctor” if they don’t hold an appropriately named degree?) Is the American-style MD an older form? Did physicians used to be actual doctors in Britain?