Why did the famous poet Zhang only save two poems?

At present, there are only two poems about Zhang, among which "Moonlit Night on a Spring River" is the most famous, which has established his position in the history of Tang poetry. There are thirty-six sentences in this poem, which depicts the attractive scenery of Jiangnan spring night with beautiful writing, and also entrusts the homesickness of the wanderer. The whole poem has a clear artistic conception and beautiful melody, which is a swan song throughout the ages. Among Zhang's poems, Moonlit Night on a Spring River is a famous work. It follows the theme of Yuefu in Sui Chen's period, and expresses its touching feelings of leaving home and philosophical understanding of life. The language of the poem is beautiful and moving, and the melody is euphemistic and long, which is completely different from the over-packaging of court poems, giving people an ethereal and quiet feeling. Natural and fresh feeling, later generations commented on Zhang Wei, who wrote this poem. The poem "Moonlit Night on a Spring River" is the title of Wu Sheng, a Yuefu. It is said that it was written by Chen Houzhu in the Southern Dynasties, but the original lyrics have not been passed down from generation to generation. Later, Emperor Yang Di also wrote this song. Zhang's poem is a quasi-topic poem. The tune of this poem is very different from the original, but it is the most famous. The specific creative background can no longer be studied.