I have a question concerning the availability of songs based on region?.

A while back I downloaded some nostalgic music and recently, even though I can still see the artist, album and songs, instead of playing through my speakers I receive a notification stating my music selection is not available in my region. Needless to say, it’s quite a disappointment to say nothing of my sorrow. Hyperboles aside, I’m really just curious what the reasonings behind that actually are.