There once was a time when a person, let's say between the ages of 15 and 30, was considered "cool" if they liked the most popular bands. The quality of a band was considered to be directly proportional to its popularity.
Today, it's considered "cool" to be into the most obscure bands and scenes. The quality of a band is now considered to be inversely proportional to its popularity. The more obscure, the more "authentic" the band and music.
At one time, if you wanted to listen to good music, all you had to do was turn on the radio to one of several FM rock stations. Now, common wisdom is that you have to seek it out, in small clubs, MySpace pages, obscure podcasts, and Austin, Texas. If it has airplay on any radio station that's not based at a college, they're sellouts that suck.
When, roughly, did this shift take place? Why do you think the rock scene transitioned from something that was shared by a large part of the population to a fragmented, insular and elitist scene -- or, really, thousands of scenes?