How do they chose what champion gets what skin?

Nightbringer Vladimir, Lee sin, Soraka Dawnbringer Karma, Soraka, Nidalee Sugar Rush Zilean, Braum, Ziggs, Evelynn Hextech Swain...

How do they chose these skins? Its almost as if they look at them and think: Can we turn this into a colorful, pink skin that is bright and has a back animation that is the opposite epic. Lee sin and Vladimir get even more dark themed skins as for they dont have a single colorful, bright skin. Meanwhile Zilean gets a sugar rush skin. Literally what everone was expecting. Cant they make more skins like nightbringer soraka just for champions that are not soraka? Dawnbringer/nightbringer zilean or swain would make way more sense. Hextech Zilean would make even MORE sense than whatever riot did. . all skins that champions like zilean will get from now on will be colorful. Bloodmoon Zilean is good but it was 4 years ago. In conclusion: Riot should mix up their skins more but in a way that the skinlines still make sense. Thats why i dont approve the NIGHTBRINGER soraka. All they release are star guardian, sugar rush, pink, colorful skins for every champion except champions like Yasuo, Lee sin, Vladimir etc. because they apparently are the only champions to have dark themes skins?

Mix up ur skins riot. Pretty sure many people dont want 1000 more pink skinlines. (excuse my sht grammar)