There's a practical reason for the map to be north facing. If you use a compass, the needle points north. So, if you then orient your self and your map facing the same direction, it's easy to figure out headings and bearings because they'll match what you see on the compass. Even in the southern hemisphere, compass needles still point north. So, orienting maps north seems like a pragmatic thing to do.

They also point south. If you changed which end of the needle was painted red it would be just as useful for orienting to the south as existing compasses are for facing north

The needle is pointing to the magnetic south, which is near our geographic north.