The Tomb should be swarming with demons but blizzard left them out. ToS literally has more Murlocs than demons in it, for the same reason it's a virtually pristine elven temple instead of a twisted ruin, because Blizzard didn't want it to feel too similar to Antorus or overdo the demons.
Basically it's an unofficial retcon - gameplay over lore. They deemed it more important to have variation for variation's sake instead of consistency and lore.