Her champ model was quite different than her splash in terms of the color palette and dint really represent her characters lore.
So riot touched it up and gave us the jinx we know and love today.
However, the discrepancy between the 2 new Mecha skins splash arts and actual in game models is 10x more glaring than Jinx's was.
Please riot, do a touch up pleeease to match the amazing art you've made. The skins will sell a lot more this way and make a lot of people very very happy.