Just my thoughts...

Consider the way we speak to new born children when encouraging speech, whether we mean to or not we incorporate musicality and melody into it. I think this makes a good case for music being a fastener for accurate recall and repetition and subsequent language use. The first words children use are often thusly musical, like dada or mama etc.. Since that is an evolutionarily valid reason for doing it it may be that it is encouraged, and as a side effect we are receptive to, and rewarded by that same melody/music even removed from speech and communication.