"The music comes from Act III of Richard Wagner’s opera Lohengrin, and by purely musical standards may be rich and profound. But the plot follows the contorted twists and turns of almost any opera. There is magic, deceit, trickery, superstition, love (of course), and ultimately the death of the unhappy lover."
(Act III Run-down from Wikipedia) The bridal chamber. Elsa and Lohengrin are ushered in with the well-known bridal chorus. They express their love for each other, but Ortrud’s words are impressed upon Elsa, and, despite Lohengrin’s warning, she asks the fatal question. Telramund rushes in to attack the knight, but is slain by Lohengrin, who sorrowfully turns to Elsa, and asks her to follow him to the king, to whom he will now reveal the mystery
…so I guess given the circumstances of the music and given the wide variety of equally beautiful musical pieces, they’d prefer you pick something more inherently in tune with the sacrament.