This was mainly because of the change of the nature of inheritance for Kuge (Court Nobles) families, as in Samurai families, to avoid property dispersion and limit the inheritance only to the legitimate children.
これは公家の間でも所領の分散化を避けて嫡子のみに相続させるという武士と同じような相続形態に変化したことに伴う側面が大きい。