Running Catch Dogs

I have no experience with greyhounds, only what I've learned by research and been told by people I feel like give good information. I've been told that one semi decent hard grey bred to another might not produce dogs that would kill a rabbit but would run one and catch it, just might not kill them. I found that interesting.
A greyhound is the fastest dog alive as the breed goes BUT they can't keep that pace up for long distances. They have very little stamina. After a grueling run for a greyhound, their energy is zapped and zapped for a while. Coupled with this, their bones are light and thier skin is thin. Why would you want to cross this dog to be and RCD when the planes states are full of stags guys breed specificly for running down and killing coyotes. They are almost greyhound fast but have more stamina, thicker skin, heavier denser bones, are bigger more powerful dogs that are bred with the specific purpose to kill stuff that fights back. Plus their is no show stock because they aren't a recognized breed thank goodness, but are a very old breed bred for that have been kept in the hands of people who work them.and USUALLY breed best to best for their hardness, speed, and endurance. Plus they are all intact males and females and are easy to get. So my question is, why do some go the route of crossing a greyhound to thier dog in order to get an rcd and not cross a stag instead?