What is poetic is what is musical in language, and musicality can be accomplished by different means. The Greeks and Romans used complex meters based on syllable length; the Psalmists parallel structures; the Beowulf poet, alliteration; the medieval European lyricists, rhyme. What we see in Europe as languages slowly shift from highly synthetic to more analytic forms is an increasing interest in rhyme as a musical device. Among inflected synthetic languages, where word endings are used to indicate a word’s function in a sentence, rather than word order, rhyming appears to have been so common as to be unpleasant and avoided. On the other hand, in an analytic language like English, a small pool of true rhyming words is a strong constraint on the free flow of expression. There must be a zone, then, where rhyming provides enough options to allow flow and clever combinations but is not so common as to be awkward or unpleasant. Again, with no statistical information or study whatever, I believe English to be slightly outside that zone, hence the proliferation of near-rhyme and assonance as alternative practices.