Meter and rhyme must be suited to the poem's content, theme, and tone.
Analogies are a staple of standardized tests. The PSAT, ACT, GRE, TOEFL exam, SAT, and FCAT, to name a few, contain significant analogy sections on the tests.
The author most likely includes this information to help the reader infer that Esperanza’s mother is not able to travel much.