Pretty simple actually. I am an Ashkenazi jew btw.
First of all, Sephardic Jews aren't known for being significantly more intelligent like Ashkenazis. The reason for this is, despite being more intelligent than the non-whites that they are genetically similar to, the bar is too low for that to make an overall difference. The difference in IQ between Sephardic and non whites is similar to the difference in IQ between Ashkenazi and the eastern European whites we are genetically similar to, meaning that Ashkenazis end up being significabtly above average overall.
With that out of the way, heres why that difference is there: Torah, and Talmud. Torah is the written bible, while Talmud is our oral tradition. We are commanded by God to read from the Torah, and the Torah is well known for being God's ultimate gift to our people. Torah is the reason why we are God's chosen people: if you are a man, you can not be a good Jew if you are an illiterate fuck, like the majority of humanity has been throughout history. Stupid people who can not read can not be Jewish. For countless generations we have taught our children how to read Torah, and by keeping ourselves literate we have maintained God's blessing over our people.
Similarly, in our tradition, the most revered Jews of all time are not those who have expressed amazing feats of faith like in other religions, but rather those who have argued against everything, and questioned every single passage of the Torah. That is Talmud, and it goes back to Avraham Avinu, who argued against God Himself. Besides creating, saving, and preserving life itself, there is nothing more holy than to engage in Talmud by arguing against Jewish Tradition.
Our long tradition of questioning everything obviously leads to supreme intelligence, and when the time is right, fundamental mathematical truths.
