[zanny]

Because they aren't perfectly good. Humans eliminate predators around the world because they threaten our livestock and public safety. If we actively wanted to cull deer populations with minimum effort it takes very little effort trap or poison them en masse versus trying to track them with rifles.

But some people find it to be a fun activity to kill wildlife and thus the whole culture of huntsman persists. People pay for the recreation of hunting. It actually makes some communities money - private citizens cull the deer while paying for the privilege.