How does Riot decide who gets the championship skin?

SPOILER ALERT: The new Championship skin is for Kalista. Why is she receiving a Championship skin? I have nothing against the champion, I just think she's one of the worst choices possible from a design perspective. For one, she's already blue. Oh man, you made her MORE blue. Fancy. Second, she has barely any particles at all. She gets a brighter spear, she gets blue ghosts. AMAZING. There are so many other champions that could do so much more with a championship skin. I was really looking forward to getting this year's skin since I don't have one yet, but now that I'm just getting a chroma skin as a Championship skin, I don't think I'm going to be making this purchase.