Wordpress must have followed some existing guideline. For example, wikiHow instructs the following for preparing poems for publication in a magazine:
- one inch margins on all sides
- poem title centered or flush left
- poems are single spaced
- Justify and indent the text of your poem.
The font they use in the examples is some Courier variation (monospaced font), and they suggest 12pt.
Choose 1-inch (2.5-cm) margins and a 12-point font. Typically, publications want wide margins so that the text is easier to read. You should also choose a standard font that doesn't distract from the poem. Courier is a good choice, and standard for some publications.
Those guidelines come from Writer's Digest, which could be where Wordpress got it from.