Because it's full of folky lullabies like Billy 1 and Knockin' On Heaven's Door and gorgeous guitar instrumentals like Bunkhouse Theme, me and J used to fall asleep together listening to this soundtrack. Eventually I walked down the aisle at our wedding to the first song on the album, which you can listen to below.
If you have any affinity for folk music, the wild west, Bob Dylan or really just a soul in general.... you are gonna wanna pick up this album. And then listen to it. Over and over.