You write the poem, and it becomes this absolutely immutable, static thing on a page. At a poetry performance nobody imagines it that way. Everybody reads their poems a little bit differently each time. So the process of tuning up becomes what the activity of poetry is. It's also this tuning up in public before other people and with other people, which is a very different kind of exchange.
Different poems demand different kinds of vocalization.
In respect to the quality of poetry, very often poets dislike actors reading poems, because they read them too well. It's hard to explain why that is, but it's a common dislike. Or to review poetry readings as well as poetry books. Or to review the way people read their work in the context of also reviewing their publications. Don't leave out the performance dimension when you imagine what the work of a poet is in critical contexts.