I've done studies on this, and even wrote my college grad paper on this very subject. Without giving you guys my entire 25 minute presentation I'll break it down quite simply.

Old male giraffe is past it's prime, and no longer reproducing. Old male giraffe is using up resources that are valuable to those other giraffes which are still reproducing. Old male giraffe will soon die of disease or old age. Concession ownerhas the option of letting old giraffe live another year or two and die of old age, only to receive no compensation for dead giraffe. OR, concession owner may have American hunter come in and hunt the old male giraffe and receive monetary compensationfor the hunt, for the taxidermy, as well as utilize the meat from the giraffe to feed guests and other people. BTW, giraffe meat was the best tasting of all game I had when I was in South Africa.