Why does the preface to Mao's poetry anthology and Zhu's annotation to the Book of Songs distort and deny the love poems in the Book of Songs?

Limited to traditional Confucian classics. Mao's Preface to Poetry is deeply influenced by the thought of "poetry teaching". He not only interprets the love poems in the Book of Songs from the perspective of pure literature, but also thinks that the love poems in the Book of Songs belong to "obscene poems", which are still confined to the Confucian classics of traditional Confucianism, namely "benevolence" and "ceremony", and denies these affectionate love poems with ethical concepts. There are many poems describing the love between men and women in The Book of Songs, which are straightforward and contrary to the Confucian "rites".