Mark Scroggins more on polonggevity.
Obviously I'm more caught up in the megalomania of it than some.
That modulated-defensive note from LZ which Mark quotes : understandable, but not an explanation for the phenomenon. There are a lot of interesting technical problems with the 20th-cent. long poem. If the ambition & the desire outruns the supporting framework (plot, thematic development, argument, stylistic variation, etc.) the poem becomes a kind of sponge.
Trouble is, sponges are endearing. Walt Whitman wrote a sponge. There is a tremendous pressure to integrate & unify the process into a life-work.
Some lazy heat-wave thoughts: vertical/horizontal = height/breadth = refinement/capaciousness = Zuk/Olson = Dante/Shakespeare...
Pound's mania linked to Dante's altitude, the view of experience as an embattled uphill climb, the exile's sense that the world-economy is skewed & inimical.
Shakespeare, on the other hand, speaks from a dramaturgically-realized inner equilibrium (rooted in poetic number). Order is the norm : tragedy & comedy are interrogations of social anomaly - disturbances of an ultimate calm. The fact that he was part of an authorized royal-aristocratic theatrical pageant meant that his ironies are always couched in, moderated by, a conservative assent to traditional order.
Pound's attitude stemmed from a decisive technical problem or contradiction. His classicism/archaism, Nietzschean/pagan power-worship was applied as a literary weapon to chastise & excoriate failed (European) civilization. But the role of the Nietzschean avenger-prophet was deracinating : it uprooted Pound from his own American background. He was unable to draw on or benefit from the liberal-democratic alternative to the wasteland of decadent & war-ravaged Europe. So he ended up as zoo exhibit in Pisan cage & Washington nuthouse : fighting a war with the new democratic power which had already rendered his authoritarian allegiances irrelevant.
But then, where does that leave the "long poem"?
Olson, Zuk & WCW came up with their alternatives. Crane had already done something completely different.
We have to look long & carefully at the underlying conceptual choices, literary allegiances & attitudes of these different American writers (& others!), to even begin to consider how the "long poem" or the culture-epic could be re-designed.
Mandelstam toward the end of his life began to formulate notions of poetic practice as "journey" and "kinship" (see Mandelshtam's Poetics by Elena Corrigan). The Dante that emerges from his "Conversation About Dante" is a very different practitioner and a different personality from the Dante of Pound & Eliot. Dante emerges, not surprisingly, as a kind of Ital-Ren. Mandelstam : a wandering, uncertain bird-man, a Chaplinesque-ecstatic Acmeist-Futurist.
The shadow of the poet (Pound's shadow, Olson's Maximus, Wordsworth's ego) is identified with the filtering mask. The mask shades and patterns the experiential universe. Whose world do we inhabit now? The world of the mask of Mandelstam's Dante?
The shape of future poems might depend on some such thing.