It's the same thing that killed the hipppie movement. Early on, the music was 'about' something. Then it was incorporated and became a Madison Avenue tool. It was manufactured and marketed. The same thing will happen, and is happening, to metal.
It's become 'associated' with things.
So bands coming up through the ranks now are trying to push that envelope even more. More outrageous acts, lyrics...etc.
On the plus side, metal will have it's re-birth again as a respectable music form like when Nirvana brought rock back from the abyss that was eighties synthie-pop.
Of course, I could be wrong. :)
[FONT=Tahoma]"All I can do is be me ... whoever that is". Bob Dylan [/FONT]