Writing in The New Yorker (Music To Your Ears, January 28, 2013), Adam Gopnik explains that there seems to be two "systems" in the brain that respond to music. One system responds to the pleasant sounds of the songs we already know and is called veridical, taken from the term meaning the degree to which an experience, perception, or interpretation accurately represents our understanding of reality. The part of your brain that lights up when you hear a familiar tune is responding to the veridical system.
The other system is sequential and anticipates the next note or harmonic move in an unfamiliar phrase of music. The sequential system is stimulated when music follows the logic of the notes or surprises us in some way that isn't merely arbitrary. The part of your brain that light up when you "get" what's happening in a piece of music you never heard before is responding to the sequential system.
Neither system is inherently better than the other, but another way of phrasing the problem with the nearly infinite amount of music now instantly available via streaming services like Spotify or on YouTube, or from any of a variety of other sources, is that we tend to make snap judgments whether or not we like something, and don't give something new or unfamiliar a chance. Why would we when we can simply just click the next selection and be instantly gratified? It's the complete domination of the veridical system over the sequential.