Yeah, but radio stations still play Nirvana. MTV devotes entire nights to Nirvana tributes.
Since Nirvana, Anthrax has put out three of the best albums that I have ever heard, but unfortunately, noone else has heard how great they are because of how bands like Nirvana changed the environment. Anthrax is still alive, but few besides those of us on the board know it.
Since Nirvana, Metallica has altered their style to maintain their time in the spotlight. The result is two "Loads" of shit, and them playing with the symphony. The Metallica I once knew and loved IS dead.
[Begin rant]
As for your earlier comment about heavy metal being kept in the underground...it's true, who wouldn't want to see their favorite band playing in a small venue instead of a large stadium. But eventually, they're not going to want to keep playing small venues and struggling to survive, they're going to pack it in, and in the end, the fans of the genre do lose. Sure, some of the over-the-top stuff in the eighties was corny, but I'll take glam-metal bands like Poison over Limp Bizkit any day, and I'll take the indulgent excesses of Guns'N Roses over paint-by-numbers bubblegum rockers like Smashmouth. And as great as Anthrax is, as long as they are ignored by the mainstream, noone is encouraged to copy that style, and somewhere along the way improve upon it. Instead, we've had hundreds of clones of safe, conservative bands that have put out forgettable pop tunes that will not be remembered five years from now. The Beatles, Led Zeppelin, Black Sabbath, Metallica...they didn't kill anything, they made music grow around them. Nirvana helped push things backwards, shrivelling up the industry in the process. Nirvana isn't the only band to blame, but I sure haven't had much to get excited about musically in the past decade as I did the decades before it.
[End rant]