I think that organ sales are substantially more complicated than this conversation is making it, but your point here could not possibly make less sense. It should be obvious with a moment's thought that "My family and I will starve right now" is way worse than "there's a small chance my second kidney will fail and then my family will starve" (and that's without considering the effect on the person who got a transplant).
Until the poor African's one remaining kidney goes bad, he can't get a transplant (nor the lifetime of expensive drugs to retain one), and his family starves for lack of a breadwinner.