The thing is, with VGUs, especially big ones like Poppy or Sion, they essentially have to make several NEW skins based on her old ones.
Sure, they don't technically get any new skins, but the workload on the skin team for remaking all 6 of her skins is almost the same as releasing 6 new skins.
The ideation phase and part of the conceptualization phase could be skipped, but everything else is just as much of a pain in the neck.
She will get one eventually, but she will probably have to wait about as long as Sion, unfortunately.