The difficulty of ancient poetry is to write down the whole text and find the connection between the paragraphs. For example, Zhang's "Moonlit Night on a Spring River" is difficult to grasp how to translate, which is a bit of a stream of consciousness.
Tang Bohu's Song of the Peach Blossom Temple is catchy and easy to remember.
At the same time, Bai Juyi's Song of Eternal Sorrow and Li Bai's Will Into the Wine are easier to remember.
But it is also related to the popularity of a poem. Just like a poem that is not a household name, it is difficult to remember if you sing less.
As for Li Sao and The Book of Songs, there is a heavy gap in language meaning, so they don't belong to this category.
First of all, memory is related to the stylistic environment. Secondly, we can easily remember the performance of a classic movie, such as Stephen Chow's movie. But what words do you remember from Jackie Chan's movie dialogue? So it is also related to the essence of poetry itself. Finally, everyone's efforts.