rant: why would anyone kill a lion that wasn't attacking them?

Just now catching up on the news, specifically, about Cecil the lion. If you're as upset about it as I am now, just skip this post.

Oddly enough, since I became a vegetarian, I am LESS opposed to legal hunting of deer, for example, because at least the animal probably had a good life in the wild before being killed (fairly quickly by a bullet and not a pack of wolves or coyotes)  vs. animals living their whole lives in horrible conditions in some factory farms.

But WTF, man. What kind of p...