Nom, because Hashem wants more than anything for us to learn His wisdom; learning is not a hecsher mitzvah in order to know what to do flr mitzvos; if it were, then you’d be asking a good kashya.
but that’s not what Torah lishma is. Torah lishma, says the rosh, brought in nefesh hachaim beginning of shaar 4 is learning leshem hatorah, to know what it says there, because we want to know what Hashem gave us.
The beis hevi criticizes the idea harshly of Torah just being a means of knowing halacha, and says that this was the sin of bayis sheni, when they didn’t make a bracha on limud hatorah, because they held it was not choshuv for its own sake, and was merely a hecsher mitzvah.
We learn because this is what Hashem wants us to do, and the reason wh He wants us to do it is mainly the above,and we get closest to Him though learning lishma.
Despite the verbiage of your posts, you’re betraying a very superficial understanding of what it means to learn and to serve Hashem in general.