If the harem concubines have no children, why should they spend the rest of their lives in Ganye Temple?

This is not the reason for not having children. It was the royal system of the Tang Dynasty. After the death of the first emperor, although the concubines in the harem didn't have to kill martyrs, they couldn't marry anyone else, so they had to be nuns in Ganye Temple, because it was a royal temple at that time. The most famous is Wu Zetian, who was sent to Ganye Temple after Li Shimin's death. It was not until about three years after Li Zhi ascended the throne that Wu Zetian was taken back to the palace by Li Zhi.