These items only drop in zones that belong to the base game. That means basically half the places in the game don't drop these. More specifically, they don't drop in the half of the game players tend to spend significantly more time in. Is the possibility of alternative material drops, such as Nirncrux in Craglorn, Casserite Sand in Wrothgar or Rogue Soot in Hew's Bane, really still a reasonable justification to not allow these items to drop in those zones as well? Most DLC zones that came after those don't even drop raw style materials from crafting nodes anymore and even if they did, the drop chance of Aetherial Dust is so low that it shouldn't even matter that something else also drops from those nodes. The drop rates of items like Aetherial Dust or Mourning Dew is another question entirely (same for the Aetheric Cipher and Chef Arquitius's Lost Thesis) but suffice it to say that they are way too low to actually properly serve their purpose (especially with the PvP ones you're probably going to hit rank 50 long before you get everything you need for the White-Gold War Torte). Please, ZOS. Reconsider your approach to these items.