In an anti-glib fashion I will reply to your query.
I think Eliot was trying to make some sense out of The Waste Land. Pound had
knifed it by more than half its length and Tommy-boy was trying to give some
sense of that inherent nonchalant loss. "Gerontion" would've been an
interesting forward to the poem if it weren't for the earlier poem's inherent
Alzheimeric anger (though connect "Gerontion" and Tiresias and you get an
interesting insight into Eliot's perception of his Elders). Eliot also
wanted to distance himself from the poem at any cost, hence the notes. The
inclusion of "Gerontion" would've further made that separation. Pound didn't
really see a problem with the personal in The Waste Land, and I would think,
knew the difference between a poet who uses emotion from their personal life
and a sophomoric personal poet (speaking of knowing the difference, anyone
know what Eliot or Pound thought of Plath? She is greatly indebted to Eliot
but I wonder if he ever saw her stuff).
Hope this helps a little,