By adding things that mesh with the lore. I could possibly see these guys living in Akavir, but they just don't seem...right for a Tamriel setting.
Yes, but cannibalistic spirits would be unlikely to live in places where "people would never go," it would cut off their food supply, which even if they didn't need they'd likely eat for satisfaction or enjoyment. I find it likely they would live near lightly populated areas to have a reliable source of food/game. Saying that they just popped out of the woodwork is a poor way to implement anything, especially if there have been other monsters implemented like that in the past.
It just doesn't promote contingency or a sense of realism to the game.
hmm yes I see what you're saying, when I said they were in slumber I meant asin dormant, like suspended animation, they are spirits after all. A quest then to stop an evil witch who is trying to create an army of werewolves by warping men and women with black magic, but something goes wrong and they retain the body of a man but the ferocity of a werewolf. The Dragonborn has a choice to kill them or to let them live, (however some escape and breed over time in both instances and those are who you fight in Skyrim's forests.)
For me it makes a little sense mechanic wise when you think that we have numerous enemies local to the frozen regions of Skyrim but not as many purely local to areas like the Rift and the Reach. Like the Frozen regions have the Frost Troll and the white frostbite spider, ice wraiths, wisp mothers etc. For non forested regions we have a normal troll, and non frost versions of wolves, sabre cats, bears etc. Besides Trolls and Spriggans the forested regions have very little in the way of indigenous threats. I think adding a wendigo at level 40-50 with a lot of health and a crap tonne of damage resistance and a really high pitched howl that sounds more like a shriek than anything else (ties into the fact that they were intended to be werewolves.) As someone mentioned before Bethesda really should add a horror element, I love suspense haha. We know they can do it, remember the Dunwich building in Fallout 3? That [censored] was terrifying lol