Yabia, after the Inquisiton in 1492, Sefardic mesorah began to change radically integrating with the people where they moved to. Also since 1492 Torah leadership of Jewry was effectively led by vastly numerically greater Gedolim of the Ashkenazic world. No one is saying the Sefardic world had no Gedolim since then, of course, but overall the leadership called from the Ashkenazic world.
After the Sefardim left their countries of origin in the aftermath of WWII, they basically followed the leadership of the Ashkenazic Gedolim in Eretz Yisroel to rebuild their Torah world. Hence the Sephardim adopting the Ashkenazic form of dress (both Rabbinic and lay), going to Ashkenazic yeshivos (including most Sefardic rabbonim when they were younger), etc.