Adaptations of hymns

Lots of Christian rock bands have adapted old hymns into rock songs, but there are some mainstream bands that have done that too. Two come to mind from the last few years, but I'm sure there are more.

The first example is based on the spiritual "Roll Jordan Roll." Here's one performance of it. Alexisonfire did an adaptation of it with different music but similar lyrics (although I'm not sure if they wrote the verses) called "The Northern." Here is the music video.

And then as a contrast, there's a Shaker song called "Simple Gifts." Here's a choir performing it. And then Weezer came along and adapted it into a rock song, loosely based on the original tune. But they didn't retain any of the lyrics. They didn't even write lyrics in the spirit of the original song. Instead of a song celebrating humility and simplicity, they adapted it into one of the most awesomely arrogant songs of all time. I can only hope they were joking. Here it is: The Greatest Man That Ever Lived (Variations on a Shaker Hymn).

(That video reminds me, ski season starts soon!)

What is it about these hymns that inspire rock singers--who don't claim to be Christians, as far as I know--to adapt them?