You can't call it a spade until you have it your hand and show it when called. These are mysterious disappearances. Nobody knows what happened. Some of the mysteries demonstrate baffling evidence, and some offer no evidence at all. As an author telling of such mysteries, he's wise not speculate on cause. He's presenting a story, and people are buying it. The audience will ascribe it to sasquatches, killer bears, little green men, werewolves, etc. I ascribe 99% of them to drownings, falls, and exposure. The remains are simply reclaimed by the environment.
Snow makes survival tougher, but it tends to help trackers find remains.
One evening I lost my trail back to my vehicle. It was late October; no snow yet, but nighttime temps got down to 20.......or colder. All I had was a dog, my rifle, and the clothes on my back. It got dark. I was only a mile or less from pavement, and the direction was obvious, but in the dark I started falling over deadfall hidden in the tall grass. Damned near broke my leg once. I was just getting to the realization that I was going to be sitting there all night feeding a fire when I broke out on a trail. It led me to my rig. It made me remember that the wilderness is a short walk from your vehicle, and the wilderness can and will kill you without mercy or regret.........quickly.