Why do I always get the same champ in hextech

Question is straightforward. Basically I keep getting Kayle skins, I started playing her some as a result but in the past two weeks I have gotten Aether, Riot and pentakill Kayle. I don't do hextech chests often so it is common that I get a kayle skin. Is this just truly luck of the draw or what? Is there a way to increase my chances of getting a champ that I do play a lot?

Thanks