Why is Du Fu's poetic style "gloomy"?

Du Fu's poetic style is called "gloomy and frustrated" because his poems show deep concern for the times, deep thinking about social reality and deep reflection on his own destiny. In his poems, we can see his concern about social injustice and people's suffering, as well as his feelings and thoughts about his own destiny. His poetry is concise in language, profound in artistic conception and sincere in emotion, with strong appeal and ideological content.