It is an interesting question.
Take 'The Wasteland' for example. How is that written so that you remain interested in it despite it being (for most people) utterly confusing? (Could be an open question as to whether people WOULD read it if they didn't know how important it is. If it was written by Joe Bloggs not T.S. Eliot.)
"April is the cruellest month" is a killer first line, not just because of how it fits into the whole poem, but the counterintuitive sentiment it articulates. At least for somebody already interested in poetry, there's a confounding subversion here of the traditional poetic equating of spring with rebirth, love, joy. And probably if you read through it you could pick up all sorts of these lines which keep people strung along, even if they can't make head nor tail of a lot of it.
I think Eliot was a master at keeping people hooked, in spite of his forbidding reputation. "Let us go then, you and I" instantly piques your curiosity, you're being taken on a journey — and then the evening is "spread out against the sky like a patient etherised upon a table". Before you read that you'd never seen that sort of comparison or even imagined it could be made.
Obviously Prufrock is a lot less challenging than The Waste Land but...