I’ve seen a couple discussions critical of the lack of shamanism in the shadowlands and how it’s bad writing, etc. Having played a shaman from the beginning, this is my theory as to why shamanism isn’t referenced.
Bluntly put: souls of ancestor-worshipping cultures don’t go to the Shadowlands. They are “earthbound” spirits.
Orc souls go to Oshu’gun or burial grounds explaining why the orc population on Azeroth doesn’t have problems practicing their religion. The same applies to Draenei, whose souls either went to Auchindoon or family shrines.
Trolls practice mummification or keep cremation urns in vast necropoli, and as we’ve seen in every troll-themed dungeon/raid, that’s where their souls stay. Tauren souls are connected to totems and burial grounds.
Pandaren, I assume, are similar. Since their culture is heavily based on Chinese, and there are shrines everywhere in Pandaria, I’m guessing these are ancestral shrines.
Night Elf souls turn into wisps and live in sacred groves. It was only because Elune chose to send them to Ardenweald that they wound up in the Shadowlands.
I don’t know if religious beliefs of Blood Elves and Goblins have ever been detailed. I also don’t know how being a descendant of a titan-forged robot affects one’s soul.
During the recent save-uther’s-soul quest line, I saw a lot of souls trapped in Torghast from all races, I interpret this as the Jailer sending mawsworn to suck up as many souls as possible, stealing them from their ancestral shrines (further evidence being Bwomsandi hiding as many souls as he could find).
Anyway, if the afterlife were an onion, ancestors are on that layer that’s closest to the living world, so they’re not really in the shadowlands. Wisps are totally in the living world, troll mummies are one step beyond that, and ancestral spirits are the next step, but still not in the shadowlands because they’re still connected to life.
If I’m making sense. Summing up: the reason shamanism doesn’t play a role in the Shadowlands story line is because ancestral spirits don’t have any power there, not being on that side of death.