One of the reason was that there was a risk of Kamakura being attacked by FUJIWARA no Hidehira and Takayoshi SATAKE, the other was that Kyoto would not hold such a large army.
その理由として、一つは藤原秀衡と佐竹隆義に鎌倉を攻められる恐れ、二つは数万騎を率い入洛すれば京がもたないとしている。