Why might a line of poetry be described as musical

It is a described as musical because it is form of literature in which the poet uses a unique style and rhythm, to express intense experience.

Explanation:

Poetry uses an artistic way to communicate something special, i. e. a musical intonation of stressed (long sounding) and unstressed (short sounding) syllables to express or describe emotions, moments, ideas, experiences, feelings and thoughts of the poet to the audience. The structural components of poetry include lines, couplet, strophe, stanza, etc.