Similar reason why the earth north pole is actually a magnetic south pole :) It was decided by convention / definition.
For those whom it isn't clear what I mean. Compass magnet's north poles point north, which is only possible if the earth's north pole is magnetically a south pole.
For those whom it isn't clear what I mean. Compass magnet's north poles point north, which is only possible if the earth's north pole is magnetically a south pole.