Giving old skins something new

Hey everyone, one thing that i have been curious about since riot has started to revisit old champions and give them new textures and VFX, why don't they go back and give some of the older legendary skins or ones that don't have them, recall animations. For example Brolaf and Gatekeeper Galio both lack recall animations or new emote animations. Is there a particular reason that you don't go back and change it. I totally understand that you want to focus on new projects but it seems like it would be a worthwhile investment to upgrade some of those skins.