WHAT WE THINK ABOUT WHAT YOU THINK ABOUT.
This is a fact of branding. Smell is the greatest driver of sensory memory. Music is the element that sets mood.
I have friends who pretend that music is an inert blank slate. You set some words to some music and there you go. The words are what matters, they say. They are, respectfully speaking, wrong.
The particulars of the music have everything to do with two important issues: how well you remember the lyrics (mnemonic), and how you feel about the words (emotional).
The first is famously illustrated by the fact that playing the following G, E, C in chime sequence will cause the unsolicited response, "N...B...C" from most Americans over 40.
The second is probably more important and far less accepted.
I had a friend in college who played in a band (The Khaki Sweat Band), which did a rendition of Stairway to Heaven to the tune of The Beverly Hillbillies Theme. The twist made the classic rock anthem into a superficial little ditty. Putting those words to that music caused people not to take them seriously.
Dark music will give people a sense of foreboding about the lyrics (no matter how happy the lyrics might be). A half-step upward key change before the final chorus will make people feel that they are participating in something important and uplifting. Stick a IV-I cadence on the end of anything, and western ears will hear it as the ending of a piece of sacred music, and attach "Amen" to it.
To see music as a neutral carrier for lyrics is naive. It is one of the many ways people fail to understand both the power and potential danger of music.