Because I hate the role they played. Pantera played a very big role in the '90s metal scene and I hate them, too. Emperor and Mayhem actually strove to become tighter, more talented, and more ambitious with each release (compare De Mysteriis Dom Sathanas to Deathcrush or Anthems to the Welkin at Dusk with Wrath of the Tyrant), Darkthrone threw all of their musicianship and songwriting ability out the window and released droning, repetitive music that "hypnotizes" some people but only serves to bore the hell out of me.
Darkthrone are a bore to listen to, and so are Varg and all of their followers. I'd just pass them and Burzum up as not worth consideration except for the fact that they hold more influence than just about any other black metal band ever, Mayhem included.