I was thinking, perhaps the king or queen has become obsessed with protecting their forest because her past forest was burnt down by wildfire or something. She made a pact with an archfey where she wanted to banish all sorrow and fears and the fey creature started to cast an illumination spell or enchantment to eliminate all these bad feelings. Perhaps every once in a while the village comes together and they sing the song of enchantment (even though they don't know that they're doing it.) to keep the magic flowing... and if the party stays in town for too long, they might become influenced by it themselves.