Actually there was an interview where the developer talked about it. See: And:
Citations of those two items:
Weapon attachments were not added to the game because "[Darktide] isn't COD, nor was designed to be COD." - Fatshark Hedge
Warhammer 40,000: Darktide to Have Customizable Characters, Left 4 Dead-Style 'Director' AI | TechRaptor