In part, I understand why. I have seen and done a fair bit of teaching. Not all of it, either seen or done, has been good. A lot of what has been less good has been about poetry. Many teachers feel that poems, to be well and truly understood, have to be dissected, flayed out so that their inner workings can be intimately viewed. And it is true that there is much to be gained from doing such a thing; just as much of our knowledge of anatomy derived from cutting people open (not always after they were dead), much of how we understand poems comes from what we find when we pick them apart.
The problem comes about when teachers--and I have fallen into this trap myself--drop their students into full-on scansion and explication. Early on, students are not equipped to be able to do to poetry what a detailed scansion or in-depth explication require; they are students for a reason. The matter is not aided by people teaching who themselves lack significant skill in performing scansion.
I like to think that I do not fall into that group.
Still, inexperienced or insufficiently-experienced teachers often turn their students loose trying to pick apart one of Shakespeare's sonnets (rewarding reading, really, and with lots of good jokes) or one of Milton's, or else some postmodernist poststructuralist poetry with no rhyme and little reason. The students get frustrated, the teacher gets frustrated, and everyone is left feeling hatred for the material. And that is a bad thing.
Scansion and explication are not just applicable to "high art" poems. Light verse, such as the limerick, can also be usefully and effectively critiqued, although this is rarely done.
I suppose I should give the NSFW warning here.
A limerick is a five-line poem, rhyming aabba (lines 1, 2, and 5 rhyme together, as do lines 3 and 4), and maintaining a largely anapestic rhythm (a foot of two unstressed syllables and a stressed syllable, like two pick-up notes and a downbeat) of two lines of trimeter (three feet to a line), two lines of dimeter (two feet to a line), and a final line of trimeter. Limericks are almost always humorous, and they are often obscene, from which their humor typically comes.
An example of the form with which I became acquainted early in life (I think I was six when my great uncle first told it to me) is
There once was a man from AbasIt is an impure example, however. Certainly, the poem does have five lines, and those lines do rhyme aabba. The poem is humorous; the absurdity of glass-made genitalia and excretion of lightning resulting from said genitals percussively playing a jazz standard tends to provoke laughter. Also, the poem is obscene; explicit reference to genitalia is generally considered impolite, and the word "ass," when used other than to refer to a donkey, is typically regarded as being mildly profane--enough to result in detention when I was in middle school, but not enough to be sent to the principal's office. The poem is, if not necessarily suitable for a kindergarten-age child, not unexpected from the near-archetypal lecherous uncle with which life generously provided me.
Whose testicles were made of glass.
They'd tinkle together
And play "Stormy Weather,"*
And lightning'd shoot out of his ass.
The deviation from full limerick form is rhythmic. The trimeter lines, rather than consisting of three anapests, are each composed of an iamb (unstressed syllable followed by stressed, familiar to many from Shakespeare and sonnets, generally) and two anapests. The dimeter lines, rather than being the fairly common anapest or the extremely common iamb (like the trimeter lines), are composed of amphibrachs; that is, they each have two instances of two unstressed syllables divided by a stressed syllable, as "They tinkled together / And played "Stormy Weather," where the italics represent emphasis.
What the deviation does is promote interest--subtly. Standard forms are useful in that they provide structure and common reference points. Relying entirely upon them, however, results in dullness, and dullness is eminently forgettable. Deviations from standard forms are memorable in their very divergence from those forms. This is certainly true in history; those who are remembered are those who act other than as expected. That the equally--if not indeed more fully--human exercise of poetry would act similarly is far from unreasonable.
My doing a short scansion on a short poem does tend to raise the question of whether or not it is true that performing analysis on a thing kills it. Have I not, in such a question, drained the fun out of a nice little laughable verse by subjecting it to examination?
I rather think not, actually. Indeed, I believe that it is necessary to do good academic work to enjoy that which is subjected to it, something I have noted. Just as taking an engine apart to see what is going on with it does not preclude enjoying driving, taking a poem apart to see what is going on in it does not preclude enjoyment of the poem. Indeed, it can well enhance it; knowing more about things well-liked is often a source of pleasure itself. And, unlike the engine, which must be reassembled to function, the poem does not cease to be a coherent whole when analyzed; the text remains there to be seen, read, perhaps even eaten.
A poem is a tasty dish, indeed.
*"Stormy Weather" looms large in the mythos of my mother's family. I may tell the story sometime...