Why are most of the poems written in the 1950s and 1960s long poems?

The new folk song movement and the road of new poetry in the late 1950s and early 1960s.

1958, the Great Leap Forward movement of economy and culture took place. Mao Zedong's mass practice of creating people's mass culture is the core of this movement, which is mainly spread in the field of poetry, and is called the New Folk Song Movement (or the Great Leap Forward Folk Song Movement).

Mao Zedong thinks that the way out for China's poetry is folk songs and classicism, which is the basis for the development of new poetry, thus denying the tradition of new poetry since the May 4th Movement.