Here's why:
* Focus on syllable count: The core structure of haiku relies on a specific syllable count (5-7-5) to create a distinct rhythm and flow. Rhyme can disrupt this carefully crafted structure.
* Emphasis on imagery: Haiku excel at evoking vivid imagery through carefully chosen words. Rhyming can distract from this by drawing attention to sound over meaning.
* Conciseness: Haiku are known for their brevity and impactful message. Rhyme can feel forced or overly poetic, going against the haiku's minimalist style.
While there are no strict rules, deviating from the traditional form can lead to a different type of poem altogether. If you're experimenting with rhyme in a haiku, it's helpful to be aware of how it might affect the poem's impact.