How can I resist a thread like this?
First, the music that was largely associated with Hollywood really killed itself, by going from new and groundbreaking to cookie-cutter albums, image over music, and being so over the top that eventually people didn't want it anymore.
Music then went in four directions.
GNR was the last, great explosion of decadent hard rock. Still the same scene, but groundbreaking again, no cookie cutter albums, and music over image.
Simultaneously, the same attitude and aggressiveness that was making GNR great was also making rap a rising genre...particularly gangsta rap, which took the "danger" that used to belong to rock n' roll, and made it their own, is a less "hard partying till you die" way, and more of a "I'm going to fucking kill you" way. But if you look at rap now, 19 years after Straight Outta Compton, it's as stale and boring as LA rock had become.
There were also two big counter movements...metal and grunge.
Of course, metal was hardly "new," but as people became more and more disgusted with rock, at the time, metal had somewhat of a revival. And, again, nearly 20 years later, mainstream metal (nu-metal, largely) is stale.
And Grunge was sort of the anti-rock hero movement. That's not to say that it wasn't good (I personally love AiC) or heavy or a variant of rock n' roll. Most of the mainstream "rock" you see today has its roots in this movement and, again, it's fucking stale!
I agree with Jarmo. It's cyclical, and we're about due for a change...big time! But if you ask me, there's a strong correlation between the kids today listening to some of the woosiest crap I've ever heard and growing up in a generation where punishment is a "timeout."