Champion Key Maps

Why doesn't lol provide a way to change key maps for specific champions? For example I want my W to be smart casted for nami however I don't want it to be smart casted for Xerath and in the way that it is set up now I have to change for each individual match. I also am irritated with how you cant simultaneously have smart cast and smart cast with indicator on! An example is Nami Q wich I want to aim before I use it wich is easier with Indicator however I want normal smartcast for W and E as they need to be cast quick and not precise! Does anyone know a solution to this or why they dont have a system such as the one Overwatch has!