Toggle champion-only targeting

Alright, I know this has been suggested more than a hundred times over the years, but why is this not a thing? Why is it that I have to hold one button, while using an ability or an auto, to make it champion-only? That's basically removing one of my abilities from use in a team fight, usually the ability I actually WANT to be champ-only. Bind it somewhere other than ~ and I lose out on my R, leave it there, I lose out on my Q.