Question

Hello Rabbi Michael,
It is well known that Rabbi Chaim of Brisk said that in learning, “you don’t ask why, but what.” That is, in conceptual analysis they do not ask why there is an obligation or a law, but what the nature of the obligation or the law is (or in Yiddish: “One must understand what it says, not why”).
But I have a bit of trouble understanding this. If we take, for example, the obligation to eat in the sukkah on the first night, in Brisk they would certainly analyze whether the obligation is the very fulfillment of the commandment, such that there is an independent commandment to eat in the sukkah on the first night, or perhaps the eating is just one clause of “you shall dwell as you ordinarily live,” and dwelling is the commandment, while eating in the sukkah is merely its expression.
But even in this “analysis,” in order to find the “what,” I would first have to ask “why”—that is, why a person is obligated at all to eat on the night of Sukkot (aside from the gezerah shavah from the Festival of Matzot). Or I would phrase it differently: where did this whole idea of eating in the sukkah on the first night even come from? And then I would also arrive at the “what,” which is deeper. It is hard for me to see how one can get to the essence of the law/obligation by asking only “what.” After all, “what” investigates only what is before us, not where it came from and what its essence is.
In addition, in the way you learn, do you identify with this style of learning? And do you think this is also the method of analysis of Rabbi Shimon Shkop and some other later authorities (Acharonim), or is this something unique specifically to Brisk?