Two good reasons but (especially outside of the hard sciences) a third reason is possibly even more relevant than supporting a research career or a teaching ski

Two good reasons but (especially outside of the hard sciences) a third reason is possibly even more relevant than supporting a research career or a teaching skills. That "Doctor" title is prestigious. Your employer can pay you more, you can get higher positions as e.g. a consultant on projects, you will automatically get more of a certain type of respect and get listed to more. I am thinking of a management consultant type career here, but I suspect it is reasonably universal. Hell in some cultures I imagine it can even help you get a better choice of marriage partner. (I know it is a little bit fake, but often people's perception is more important than reality)