n0m re limud Torah: “Okay it’s a mitzvah. So is putting a fence on the porch. But why are we so consumed with it? Why is learning Torah so critical? It is what Hashem wants and nothing else. So let’s to some other mitzva instead.”
Because bittul Torah is an aveirah and one is meant to learn Torah during every free moment when one is not involved in any other important activity (such as writing in the coffee room?). And fine, if you have other mitzvos to do you are exempt from learning Torah at that time.