The practice of learning “yeshivish mesechtos” is only about a hundred years old. The purpose was to hone the analytical skills of the yeshiva bochur, with the assumption that with these skills he can learn any mesechta or subject with success. The yeshivish mesechtos are chock full of difficult theoretical concepts and serve as fertile ground for sharpening the mind.
Whether one agrees with this system or not, the yeshiva boy does not get a ptur from learning other mesechtos or halachah. He is expected to use his “free” time or shorter sedorim to learn everything there is to learn.