In those days, the Emperor with many Princes and Princesses had to allow them to enter into the priesthood while they were young, except for the candidate Prince who will succeed to the throne, this was because the Emperor could not afford to financially support the Princes and Princesses, or the court officials could not afford to have them be demoted from nobility to subject, (It is needless to say that the Princes who went into the priesthood would not have any children.
また、当時天皇に複数の皇子がいる場合、複数の親王の生活を支える財政的ゆとりが無い事や臣籍降下をさせるだけの公家官位の余裕が無い事から、皇位継承者以外の皇子は全て幼くして出家を強要せざるを得ない（当然ながら出家した皇子には子孫が存在しない事になる。