If you want lions to be dead, BAN trophy hunting. The farmers and ranchers in Africa will kill all the lions faster than you can imagine. Why? Because lions are a predator. They hunt and eat their cattle. Not to mention they are dangerous to humans as well. So, they are not viewed in the same way there. They are more like a pest.

This is how Wolves got hunted to extinction in the US.

Trophy Hunting give lions a good reason to exist for the African people. So, it encourages conservation because they like the money it provides them with. Otherwise, they will just kill all the lions anyway.