Why are there Two Systems of Tiberian Ṭeʿamim?

Why might it be that a dedicated system of accentuation is used for ‘the Three’—the ‘poetic’ books of Job, Proverbs, and Psalms—but not for the many other ‘poetic texts’ found scattered throughout the ‘Twenty-One’ (the rest of the books of the Hebrew Bible)? The earliest commentators associate the two types of Tiberian accentuation with differences in verse-length. More modern commentators attribute it to the essence of poetry. Following these two ideas, two different methods of presenting poetry can be observed in the Twenty-One. One is appropriate to poetic texts with short verses (of fewer than eight words per verse) and the other is appropriate to poetic texts with long verses (of more than ten words per verse). Within this double system, the practical challenges of presenting short-verse poetic texts under the accentuation system of the Twenty-One can be observed in the one text that attempts this feat (2 Sam. 22). This observation suggests a rationale for a different system of accentuation that is more appropriate to extended texts of exclusively short-verse poetry, as found in the books of Psalms, Proverbs, and Job, but not in the books of Chronicles, Lamentations and Song of Songs.