Here's my educated guess: Most of the issues surrounding a cadaver are related to disease, disposal, and/or desecration of a corpse. i.e. weirdo's who would steal corpses for sex toys, haunted house props, etc. Since this body was discovered in the late 1800's, disease and bizarre desecration are not much of an issue. So, what you have is a mummy that old enough to be a collectible/museum piece, but not old enough to warrant the attention of any museum. Hence, it's being held in a "private collection".