Legendary Skins

I've been thinking about champions, skins and legendary skins. and I've wondered why havent all these popular champions got a legendary? These are just some champs I thought of when i was thinking of popular champs and none of them have a legendary despite being popular. I personally dont play any of them but I love legendary skins they urge me to learn the champ if the skin interests me enough. Needless to say im very surprised that they dont have legendary skins people always talk about them yet they dont give them big skins like that I think if they gave and Rengar legendary skins at the same time maybe different themes together would be cool but would never happen given that it would probably be extremely hard to make 2 legendary skins at the same time (maybe not but idk). But I feel that if anyone should get a legendary since he only has 2 skins and really deserves one.