It's a line of progression from old metal stuff, which always had social transgression and horror elements as key themes. Because the genre is more extreme musically, the lyrics are adjusted to be more extreme, too. "Death Metal English" is actually not that common.
Serial murderers have always been a lyrical topic, for example, and you can see the progression directly if you look for songs about them. From Judas Priest and Iron Maiden writing about them existing, to 80s bands like Slayer writing about them more individually, to death metal bands in the later 80s and 90s very graphically describing their acts.
Serial murderers have always been a lyrical topic, for example, and you can see the progression directly if you look for songs about them. From Judas Priest and Iron Maiden writing about them existing, to 80s bands like Slayer writing about them more individually, to death metal bands in the later 80s and 90s very graphically describing their acts.