Champion Creation

I've noticed something quite troubling about the champions which have been created up to date. Looking at them all, they all lack something extremely important, and I find it honestly shocking that Riot has overlooked this for so long. Why is it that every single champion has exactly one head? 100% of champions have exactly one head (discounting Rengar after he has taken Kha'Zix's and Nunu and Willump who each have one and doesn't really count). What exactly makes multiheaded champions problematic? Does Riot disagree with the existence of multiheaded entities? Do they simply lack ideas on how to design a champion which has more than one head? What's up?