As a former farmer, you have to have some market for the disposition of all livestock raised by man. What else should you do with an injured or old horse? Feeding worms in a deep hole is a waste of input costs. Humane slaughter and good use of the animal's resources are what should be done, rgardless of it's attraction.
Unless it's processed, packaged, and distributed for use, it's a wasted resource which gets cleaned up by maggots.