Recently I revisited - for pleasure - Theodore Roethke's "The Waking." It dawned on me that a remarkable number of great, mid-century (20th) poets writing in English have poems that are highly anthologized and, relative to the rest of their oeuvres, relatively simple. The examples that came to mind did so for two reasons: 1) the poets were writing at a similar time period to Roethke, 2) the poets were writing a villanelle, a form imported to English from the French and becoming relatively popular at the time.
The examples that came to mind ought to be familiar to anyone beyond new to poetry; and to anyone new to poetry, they ought to be read (which will make them instantly familiar):
1) Elizabeth Bishop, "One Art"
2) W.H. Auden, "Time Will Say I Told You So"
3) Dylan Thomas, "Do not go gentle into that good night..."
Another poet and poem that came to mind was Robert Frost's "Stopping by Woods on a Snowy Evening." I'll get back to this point.
Thomas, despite the appeal of his allegedly drunken, raucous readings, is actually a poet's poet - highly figurative and not afraid to write beautifully and forget about cogency or coherence. See those sonnets about the owl for what I mean.
Bishop is stately and intelligent, literary to the Nth degree; so is Auden. Also, Bishop and Auden wrote many poems far superior with regards to beauty and complexity, bravado and originality, than the examples above. Though for both, these rank highly.
Here's why I think the poems above were written: These highly talented poets were approaching a novel form (to my knowledge) and so by virtue of that, they were taking a poetic risk. Therefore, to prevent further risk, they chose "safe" themes and stuck to simple rhymes and diction.
Bishop: the art of loss -- great paradox built on simple diction, relatively simple rhyme, and the bittersweet subject of loss.
Auden - the bittersweet subject of loss via time passing. Classic...
Thomas - the heroism of facing death bravely, the bittersweet triumph that cannot (write it!) be.
Roethke, I think, plays it less safe: The theme of sleeping / waking is LESS "poetic." What I mean by that is - Love and Death, time, the sun and moon, the stars and the sea - these are present in ALMOST every poem; they are akin to the comedian's farts, dicks and faux pas. But the sleeping-waking dichotomy is minor - the row row row your boat, what dreams may come - it echoes death but is NOT death. It is not a major trope, but indirectly it touches one, and has been used to do so often.
This is an opportune time to turn to Frost -- "miles to go before I SLEEP." Echoing the idea of unknowing and mortality without directly addressing it (although the isolated landscape and snow helps).
I think the historical confluence of great talent and new form were two strains of a three-part happenstance which lead to these pieces.
You have the novel form, provoking talented poets to make safe choices (moving in unfamiliar ground), and the novel form happens to satisfy the RHYME desired (or expected) by a common reader. On top of that, the desired or expected rhyme is decidedly NOT anything like a sonnet, providing the common reader a little bit of novelty without too much.
So in the mid-1900s, four great moderns (Bishop and Auden far-greater than Thomas who's wilder than Roethke) met a great (and possibly intimidating - to the poets at that time) form, and thus four great poems were produced. Kind of great poets taking baby steps; enacting what Roethke says in the writing of these poems: "learn by going where I have to go" -- these poets were literally taking their poetic awakening (into the villanelle dream) slow (by creeping; taking little risk).
Everybody knows Dylan Thomas's poem. Bishop's poem is in every anthology and beloved by those who know it. Roethke's poem is simply Roethke's best, in my opinion (or at least ranks very highly in a slimmer body of work compared to Auden and Bishop; the "lovely in her bones" poem also comes to mind as highly memorable, as long as some about his father's greenhouse). (To my mind, Roethke is one of those rare strong minor poets I think Bloom mentioned once (in my reading) -- like Berryman or Jarrell -- that group is highly similar in their lesser triumphs, lifetime popularity and medicine cabinets, I think. As my reading deepens, I see Berryman's celebrated Dream Songs losing influence and likely not lasting much further into "posterity." Then again, anthologies of other nation's poets are filled with weak poems relative to their shining stars - the French, the Russians. So much pales next to Pushkin and Pasternak. But it seems as you go backward, there are less and less weaklings, as if they - the minors - simply require more time to be shed: there are a LOT of 20th century weaklings in 21st c anthologies; a few less 19th cent weaklings; even less 18th c...then there are only 1-2 poets from centuries 17th and further back.) Auden's poem is probably quite popular with readers newer to poetry who take a look at Auden (as any new reader should relatively early on -- his books are at most book stores and libraries, and most general poetry reading will refer to him often).
I think I can simplify: great poets checked themselves (limited their potential hazards, simplified) while attempting a new form that would (ultimately) prove satisfying to the common reader -- This created a great poem for the common reader: Satisfying their desires (semi-novel rhyme, traditional poetic themes, toned down diction) and thus proved (for now) lasting. I think they seem - in fact, are - accessible; at least the emotion is (communicated before it's understood), as the content rarely strays from the main topic or shocks with a weird metaphor: that emotion connected to loss, O grief be its name, tragedy and despair; love lost.
I include Frost because his poem achieves something similar, though I'm not sure it's for the same confluence of issues. He writes a novel form of the terza rima, adding a 4th line to make each stanza a quatrain and ending on a quatrain. So it's a variation on the terza rima. The theme and diction are rather simple, the accessibility seems to be there. And that final line completes the terza rima in an unusual way - a couplet, actually blues couplet really: a 100% faithfully repeated line. Only again - he reminds the reader "sleep" is not just the temporary kind. Thus, simple emotion, simple diction, classic themes - all safe territory CONTENT-wise in the relative terra incognita of the Novel Form.