What makes The Western Canon canonical? The answers to this are often times equivocal and differ from one generation to the next, from one cultural meridian to the next, and that in itself is against the word "canon".
In two of his essays, "Hamlet" and "Tradition and Individual Talent" (written around 1920), T.S. Eliot argues that poets must divorce their most specific traits of personality, and those imageries that are their own and nobody else's, in order to allow themselves to work with what is called "objective correlatives" -- in other words, elements of a poetics that anybody can relate to, visions and states, chains of events from which all people, no matter how different, will extract the same unique message.
Beyond expressing just his particular self, the poet ought to play the role of a conduit, a medium, by way of which the ideas and images turn, on the side of the readers, all readers, into precise, universal emotions.
In his day and age, T.S. Eliot noticed among poets a prominence of the autobiographical, in that writers and poets were planting their own singular exotic and circumstantial musings in fields otherwise reserved to vivid, trasmissible masterpieces, masterpieces able to pierce the layers of ethos and time; and then again there was a prominence of personal emotion usurping what Mathew Arnold calls, in his definition of art, "the disinterested interplay of reason and consciousness".
That's not to say that what's needed is a poetry without emotions, but a balanced fusion of emotion and intelligence outside the realm of a poet's strictly personal experience.
And so, T.S. Eliot downgraded the poetry of Tennyson, Keats or Byron, the soft, feeling-ladden trubadours of Western Romanticism.