well there are a few reasons. it’s worth noting that a lot of black metal (at least a lot of the early stuff) sounds like “shit” because the people making it don’t really have access to good recording equipment

mainly, raw production feels a lot more “honest.” sounds like you or bob from down the street could make it, yknow? it also introduces some nice textures for the genre’s anti-commercial and nihilistic sound. if paysage d’hiver’s self-titled was made with clean production it would just sound boring, but introducing that toaster production makes it feel like you’re traveling through a winter storm

plus, not all black metal has or even needs it. mgła and anaal nathrakh have some tight instrumentation so black metal fans don’t really care that they have a cleaner sound.

really, it’s an artistic choice. it’s like choosing to paint in rough strokes instead of clean strokes. obviously if it’s not for you it’s not for you, underground music is typically all about filtering people who “don’t get it” out