Here's why:
* Metaphor is a literary device, not a poem structure. It can be used in poems of any length or format.
* Stanzas are groups of lines in a poem. The number of stanzas is determined by the poet's choice of how to break up the lines.
A short metaphor poem might have just one stanza, while a longer one could have multiple.
For example:
* A single stanza poem could use a single metaphor to convey its message.
* A multi-stanza poem could explore a theme through multiple metaphors, each building on the previous one.
Ultimately, the number of stanzas in a metaphor poem is a matter of the poet's artistic choice and the poem's overall structure and flow.