Let me put this another way;
Why would expect there to be an equal amount on both sides?
Plate tectonics moves the plates around on geological timescales. That motion is controlled by large scale forces and structures, but the net effect is that there is no preferential location on the planet for continents to exist as they drift around.
There is no preferred location, and one continent doesn’t care where other continents are. SO there is no driving force to balance the locations either side of a rather arbitrary line. So the location of the continents is somewhat arbitrary, from a statistical point of view.
SO the only real answer to why is there more North than SOuth, is basically because “that’s just how it is at the moment”. There are plenty of periods of geological history where this isn’t true. The weird thing would be if there were any substantial periods where these proportions were truly equal.
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