El nath Castle

There are no living "Zakum worshippers". How can I explain this...

The people of El Nath (or whatever town preceded it) discovered something valuable to mine in the mountains. doesn't specify what to my knowledge but it's probably something generic like Gold. Anyway, as they established a mining area up in the mountains, it eventually grew into a town of its own. However, the mines became less fruitful, and they had to dig deeper and deeper. They could just as easily have quit mining, but the townspeople were greedy and didn't want to give up their source of riches. I believe they were warned to stop but continued anyway. As they kept digging, they at last pierced through the volcanic heart of the mountain, where a terrible demonic tree had been sealed. Because of the miners' greed, the demonic tree was able to whisper to them, to manipulate their minds. They began worshipping the tree as a god, and it convinced them to build a statue in its' honor. By the time the statue was completed, Zakum's power had grown so great that he was able to inhabit it, and subsequently wiped out the surviving townspeople and destroyed the town. The Zombies at the top of El Nath are the... "Survivors" of Zakum's attack. You can think of the Dead Mine scrolls as return scrolls originally aimed at that town, but it no longer exists.

unfortunately that information is spread out across the game, vast gaps of levels apart. Granted i spiced it up a bit, but that is the real story of Zakum.

No, they're real. If you read what the quest NPCs say instead of skipping. Otherwise, you might make up a story on your own.