It is said that this was the will of their father Emperor Kanmu, who believed a hereditary imperial succession would be difficult, considering Emperor Heizei's being in poor health and his children still being young.
これは平城天皇が病弱でその子供達も幼かった事を考えて嫡流相続による皇位継承を困難と見た父・桓武天皇の意向があったともいわれている。