People like to guess a pattern (i.e. "from the first 5 secs I think the song will go like this and I'll like it") and like when they're right. That's also why we tend to like more songs we've already heard several times (even though we didn't like them a lot in the beginning).

Summary of the article: http://tldr.io/tldrs/516bfd54649fcf9e0a000de0/why-does-music...