Here's why:
* No official, consistent record: There isn't a universally accepted organization or record keeping body that tracks the tallest horses in the world.
* Height fluctuations: Horses can grow and shrink slightly throughout their lives due to factors like age and diet.
* Privacy: Owners of very tall horses may not publicize their animals or be publicly known.
While the title of "tallest horse" is a fascinating one, it's likely that the actual owner of the tallest horse in the world remains unknown!