AA and UA have better deals? Perhaps that is because they DO NOT FLY TO AFRICA. Was the UA deal for flying SAA nonstop (doubt it). Sorry but considering that the seat was first available, and the OP passed it up, shows that there was availability. Someone else then grabbed it, which is not surprising as Delta has the vastly superior product to South Africa. There are many valid complaints about Delta these days, but it would seem that this is not one of them.
Regarding China and the Olympics, almost ALL carriers played the same games, as they ALL do when there is a major sporting event on (Olympics, World Cup, even the superbowl).