Simple meaning of learning lishma (for it's own sake) is because Hashem commanded us to learn Torah. Reb Chaim of Volozhin opposed kavanahs (elevated spiritual meditations) of devykus (cleaving to Hashem) during learning. The point of learning Torah is to understand what we are learning. Baal Shem taught that when you learn we should concentrate on learning. Tanya explains that the only way a Jew can grasp the mind of G-d is by learning Torah. There is no greater act of unification then when we are clothed in Him and He is clothed in us at the time that we are learning Torah.