There's obviously no hard and fast rules but as a rule of thumb, the smaller areas tend to buy game in from auctions etc and the larger areas tend to have a surplus of game that they either sell or re locate to other areas owned by the same people.
As you say, the game in (most places) have heavy hunting pressure and that of course means they learn the area and it's escape routes in short order...... the difference with Lions is that they are only moved into the hunting areas a few days and often a few hours before the hunt, so they don't get to learn the area etc.
Of course, the best hunting is in unfenced true wilderness areas but in all honesty, you won't find much of that in SA and the SA (and similar countries/areas) option is more affordable than the unfenced options. It's also sometimes more suitable for some clients who want the more civilised option for whatever reason.