Honestly, I can just imagine a corporate money man standing over the artist's shoulder with events unfolding as such
Money Man: "Yeah, can we make it sexier? Like, I need to see some curves."
Artist: "Kayle has always been fully armoured, it's why a lot of people like -"
Money Man: "Yeah I get that, but with the success of our recent popstars skin, fans clearly want HOT champions."
Artist: "I mean, sure, but that's an entirely different -"
Money Man: "I'm glad we're in agreement! Give me some hot lady concept art when you've got it ready." leaves
Artist: sigh "Maybe I can at least keep her fully clothed..."
It would be incredibly disheartening to find out that whoever was in charge of redesigning Kayle legitimately thought that this visual representation of the character was loyal to what she was and what fans were hoping to see. It's an incredibly tone deaf decision that I pray came from the marketing department, not the creative team.