Humans love recognizable patterns and symmetry. Rhymes sound alike, and when coupled with meter, help make the words “stick” in our memory. We also like artificial things that are easily distinguishable from the chaos and entropy of the natural world. We enjoy our feeble attempts at imposing order.

I have two theories, applying not just to rhyme but to traditional verse forms in general (i.e., formal constraints like rhyme, meter, alliteration, etc.):

1. In prehistory—when all knowledge was transmitted orally—verse constraints acted as a sort of verbal checksum to prevent transmitted knowledge from getting corrupted accidentally. And the presence of verse patterns became a subliminal flag indicating that whatever was being sung or recited was important knowledge worth the extra effort of casting into verse.

2. It’s been found in many different contexts that humans are most drawn to information with a novelty-to-predictability ratio of about 20–25%: if it’s much less than that we get bored, and if it’s much more than that we get lost and/or dismiss it as gibberish. So adding a predictable element like a regular rhyme pattern gives the creator freedom to add more novel elements without losing the audience.