Why did the author most likely choose this structure for his poem?

Incomplete question. The poem ("In Cabin'd Ships at Sea" by Walt Whitman) read;

The tones of unseen mystery, the vague and vast suggestions of the

briny world, the liquid-flowing syllables,

The perfume, the faint creaking of the cordage, the melancholy rhythm,

The boundless vista and the horizon far and dim are all here,

And this is ocean's poem.

because the long-line structure allows Whitman to include a list.

Explanation:

It is interesting to note that the use of long lines in poetry often makes the sentences in the poem reveal more details; making the poem better understood.

Hence, by using the long line structure, Walt Whitman is able to include a list in the poem; thereby allowing more details to be added into his poetry.