I am not sure, but please correct me if i am wrong. Is the reason that the condtions are anoxic, which lead to lower rate of decomposing, and bog water primarily will not have stuff to digest humans otherwise (probably either stuff which does photosynthesis, or small filter feeders), so you would be kinda preserved. And if the bog is actively developing, you may descend, and eventually be stuck preserved (or whatever is the appropriate term for it)