Just because measures don't eliminate a disease, doesn't mean they are without value. One could simply ignore a disease like CWD. What would the result be? At first populations would crash. Some deer would show resistance and survive. Eventually (could be many, many years) a balance would be restored. By taking prophylactic measures, it may be possible to stop a crash. That doesn't mean populations won't drop significantly but the curve may not be as steep. Just because we can't eliminate a disease doesn't mean it is not wise to try to manage it.
A responsible person will stay home from work when they are contagious. If the disease has severe enough consequences, we may even forcibly quarantine some people during an outbreak. With animals, the only practical method may be to eliminate hot spots, whether it is destroying a herd of cattle or highly thinning deer in a specific location.
While this shouldn't be done without a lot of thought, it can be an effective management technique. No one likes it, but medicine can be bitter.
Thanks,
Jack