The historical reason for it goes back to the end of the Edo era when the class/ caste system (samurai, farmers, townspeople/ merchants, and untouchables) was scrapped. Understandably the knowledge of class didn’t disappear at the same time, and indeed it is still said that people hire private detectives to check that there are no eta (untouchables) or Koreans in their future son or daughter in law’s family. Prejudice against particular regions, gender and disability are also common, as is preference for people with a shared school, hometown etc. All this means that interviews in Japan could nicer approach any kind of fairness, even nowadays and certainly not in the Meiji period when the whole system was set up.
The other factors are:
– A Confucian trust in exams
– Not being allowed any hobbies, voluntary work etc while preparing for entrance exams, and therefore having nothing to write on a university application form