After doing a PHd, why do you become a doctor?

Question: After doing a PHd, why do you become a doctor?
- Keywords:
  education,
  phd,
  university
Asked by Zealousy to Chris on 22 Jun 2015.
- Chris Armstrong answered on 22 Jun 2015:
  
  Tradition I guess?
  Doctor is just a title awarded to those with a “doctorate”.
  
  Ironically medical Doctors are generally exceptions to that rule, as they become a Doctor after their Bachelor degree (albeit an extended Bachelor degree compared to every other field).

Question: After doing a PHd, why do you become a doctor?