First, there is a great controversy about poetry now. Without the rigid standards of Ming and Qing dynasties, it is difficult to judge whether it is good or bad.
Second, China literature is mainly in modern vernacular Chinese, while poetry is a minor category. Examination questions cannot deviate from the educational syllabus, and writing poems cannot be applied to life, which is not a basic skill.
Third: the teacher can't understand. Writing poetry requires a lot of notes to understand, which requires the marking teacher to spend a lot of time, but there is not so much time for marking the senior high school entrance examination.