I think that metal music can broadly be split between "extreme" and "accessible" (for lack of better words). Today, it feels as though many of the bands on the accessible side of the spectrum have been increasingly deriving influences from other musical genres (rock, pop, shoegaze, etc.) in addition to past metal music. Accessible metal is what is popular because it is easier to listen to without existing background knowledge. I think that the result of this is that that branch of metal music has become increasingly watered down - hence, not as good if you like metal music.
It sounds to me, however, that most extreme metal bands derive their music almost exclusively from past metal bands. Therefore their music would have a more distilled metal sound.
I guess that back in the 80s/90s there was a stronger interest in pure metal music.