: My guess is it may have something to do with Edith Bratt Tolkien, who used to sing and dance for JRRT when they young (and she was more-or-less the model for Luthien).

I seem to remember reading somewhere in the HoME that the elves sang so well because of their superior sense of hearing. Maybe that very hearing would enable them to enjoy the perfection of their own singing (which they would be enabled to enhance and fine-tune by the very same hearing) so much more because of that sense ofhearing. Also, it adds to the picture of elves as good creatures that are able to enjoy life's pleasures to the fullest, and do so.
NT