The purpose of learning in Brisk is primairily to bekoine seder kodhsim by roshei yeshiva who have devoted their lives to this seder,
If this was the primary reason to go to Brisk, there would only be a dozen bochurim. There are other roshei yeshiva who fit that billing more than the Soloveitchik. In reality, if Brisk would offer the regular mashechtos there would be more of a clamor to attend.