Why do all satellites face south?

This allows them to see the entire surface of the Earth. The Earth is rotating East to West. (Or West to East if you were the satellite.) If you placed a satellite into an East-West orbit, it would not see the polar regions. If it were high enough (geo-stationary), it would only see one spot on the Earth. By using North-South (polar) orbits, the satellites will, after several orbits, be able to see the entire surface of the Earth.