Why do movement abilities have higher priority then stuns?

So honest question here, why can't i stun a champion out of a dash/charge/ other movement skill? I see them get hit by the stun, but they are still going to travel full distance and probably also be allowed to land their queued up ability they cast during the previous abilities animation. Like i'm super freaking salty that i kept getting wrecked by a because his ultimate can literally run right through my ultimate, not to mention that he will also get his fear to proc (because that's fair).

I feel like this is a thing with all movement abilities, once they start it doesn't matter that they got hit by a root/stun, champion is going to finish traveling the full distance but the duration of the root/stun will start ticking down during their movement animation. If the champion has an offensive ability attached to the movement you can bet your ass your are still getting hit with it, because why should something like being outplayed stop you from getting to do your damage.