It's not greed, it is practicality.
If you shoot it, what do you do with 1500 pounds of rotting carcass?
Trying to do anything with a cow that has died on the ranch is a logistical nightmare. Ranchers just don't have any equipmaent to deal with them. You generally have to get someone to come with a backhoe for a day to dig a hole that big.
You have to get them into a trailer while they can still try to help. Whether you take them to a slaughter house or a rendering plant, they will be treated the same. Since most downer cows have some physical injury rather than a disease there is no reason not to eat them.
So9