It was because the state of gaka in Chokusenshu changed and waka for celebrations reflecting real life such as longevity gradually disappeared being replaced with daieika (ancient poems composed under assigned titles) and Daijoe waka (poem composed at the royal ceremony).
勅撰集の賀歌の有り様が変化し、算賀をはじめ現実に即した言祝ぎの歌がしだいに姿を消し、題詠歌と大嘗祭和歌になっていくからである。