A rule called ETOPS limits how far away from a runway a 2-engine passenger plane is allowed to fly, to account for emergency diversions. It used to only be 60 minutes, which is why all intercontinental trips were done in 3 or 4 engine planes. These days, it's up to 180 minutes (with extensions by special arrangement) which allows planes to fly pretty mucheverywhere.
Except for Antarctica. It's just so remote.
Also, get a globe out (or Google Earth) and look at the South Pole. Now try and find two destinations a reasonable distance apart whose Great Circle flight would actually cross the pole. There aren't really any. The few that just about count are nowhere near big enough to warrant a 747 or A380 (the only 4-engine planes still in widespread use)
Finally, it's just a horrible place to make an emergency landing. High altitude = high landing speed and then everyone would freeze to death.