I think it's because there are a lot of people who don't really think about music as anything more than a catchy tune to play in the background of whatever they do. This pop music is mindless and appeals to a huge range of people.
Anyone who truly invests some thought in music will find their niche somewhere, and since there are so many different genres and sub-genres all with equal talent and all making "real music", none of these will ever get attention from more than a smaller group of people. Everyone's different, and music reflects who people are, so if you're into a specific style, chances are it will never become "mainstream". It will never make much money because it's not worth the music labels' effort to promote to the degree that they do for these pop stars. Real musicians won't stop though, and will keep making music regardless of the money it makes them. It's just the way the music industry is, and I don't see it changing any time soon.