My guesses for its inclusion are that:
(1) It's a waltz. Leonard loves waltzes. We love waltzes done by Leonard.
(2) It's a longtime favourite of Leonard's. He's performed it through the years, and may have even performed it with The Buckskin Boys.
(3) It's a song that Leonard has adapted through writing a verse for it himself.
(4) The song relates to love and loss ~ two prominent themes with Leonard.
(5) The song is consistent with others on the album, as a look into the [and his] past.
(6) The song ends the album with a 'lift' in sound ~ one that actually inspires me to want to return to the beginning

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What Leonard's reasons are may be totally different from the ones I've conjectured

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~ Lizzy