Why do we need an option to report for leave/afk?

With leavebuster, but also the fact that the game aknowledges when someone leaves or afk's why is there a report option? shouldnt the game just auto report as it does with leavebuster, and since its obvious that reporting someone still allows you to play with them in the very next game why is it even an option? I could see leaving it as an option if reporting actually helped you not pair up with the person in the next match but even then the game should automatically do it for us