Why S not C

I'm one of those person who is asking why President Benigno Aquino III is using 'S' as his middle initial rather than using 'C' (Cojuangco). So i searched why is he using 'S' instead of 'C'. I found out S stand for  Simeon and part of President Noynoy 's given names Benigno Simeon also given names of his father and grand father and both uses 'S as their middle initial. He uses 'S' instead of 'C' because he is following the tradition. Although the practice is to use mother's maiden name.