my thoughts exactly, their should not be any difference between boy or girl but there is in every society around the world from the very beginning of mankind and it will stay as it is until the very end.
few reasons why:
people want son who will carry on the family name and make sure family lineage is well and alive
parents expect the son to take care of them when they are old
boys are stronger and better workers that could keep the family business alive or help dad around
Boys were just considered better than girls, its genetics because they were and are heirs to thrones
i can go on .. and on, but lets make a stop here - that’s how the world is and it will stay as it is.