Limited skins for certain champs

Have any of you guys wondered why certain champions are unnoticed for skins. For example has been around for about 1.5 years by the time this post has been published, and he has had 3 skins in the past year, probably many more to follow. Another champion like who has been around for almost 6 years, has only been given 2 skins. In conclusion Riot Games should make a pattern or a skin creation rotation, or try to equal up the number of skins for a champ, and not just focus on the newer champs. -Please share your thoughts