Mainly because Western Diamondbacks aren't indigenous to this area and the picture has the markings indicative of a Prairie which are common in our area; also gets called Western or Prairie Western (Crotalus viridis).
The Western Diamondback (Crotalus atrox), you won't see those in CCC unless someone brings it there; and it probably won't make it for very long. The diamond markings are more defined, and, though Diamondbacks have a patternless species, you don't get those brilliant contrasting blotches of the Prairie. Both can have the ringed tail markings.
Anyway, there's never a Felis catus around when you need one.