Big Willie He could have the same career threatening injury in SA, and he would certainly not be getting 1 billion. He is not guaranteed that money unless he is there 5 years (at about 200 million per season).
That said, even if it was 200 million (for even just one season), that's a lot of f*cking money. But real players want to play for the best teams, whether they have already won stuff or not. Recognition, legacy, iconic status, etc. That stuff is important to many players. Other than money, what would he get in SA?