And you could volunteer at the homeles shelter.

The way these things work, is that the people working in these places identify problem animals, like infertile males that prevent the herd, or pack or pride or what ever growing, unusually agressive animals, animals with genetic faults that could be hereditary etc etc. Basically anything that could hinder the the population of the endangered or vulnerable species. These animals are hard or impossible to relocate because most places dont want to take these problem animals in, because they generaly are bad where ever they are. I mean what zoo wants lion that kills anything they see or what animal sanctuary wants rhino that kills anything it can catch?

The park rangers could very easily kill the animals them self, but running these animal sanctuarys is very expensive so its better if they find some rich dude that is willing to pay ridicilous amount of money to do it for them.

The rich dude them self isint necessary a philantropist, but the money they spend goes to local economy and is often used for things like security against poachers, vetenarians and infrastructure.

Its easy to think that killing any exotic big game is always bad, but in reality the targets are always chosen carefully.