Pretty straight forward--why do Sephardim put on the tefillin shel yad while sitting?
Hacham Ovadia Yosef has a rule in his Pesakim- "Bimkom Minhag Lo Amrinan Kibalnu Horaot Maran- when there is a preexisting Minhag we don't follow Maran". Why is this so? Because Maran writes in the Hakdama to the Bet Yosef that he didn't come to get rid of old Minhagim. Therefor the preexisting Minhag before the Bet Yosef was to place them sitting down.