It's both. As you get older you don't have the emotional connection with new music the way you did in your formative years because the music you heard growing up is much more tied to your social development and who you are as a person. I say it's both because there are so many more artists now than there use to be and artists tend to put out A LOT more music. As the amount of music created increases, the quality goes down. And as even the best songs have shorter and shorter runs because more new music is right on it's heels it becomes a lot less memorable