To be clear they cost WAAAAY more then a new champion to make, probably like 2-3 times the amount of time resources as a new champion. I can break what it takes down very clearly having worked on many Champs/VGUS/VUs over the years
- New concept art and in some cases a re-imagining of the champ to better fit the IP (in the case of a Champion who doesn't fit as well with current lore) Jax is a good example of this. Who he was, and why he was a purple thing with 3 fingers wasn't really defined in his previous version, so we had to do a good amount of narrative/concept work to get him better aligned with the modern IP before we could even start.
- All new Model, Rig, VFX and Animations
- New VO across every language, and every Legendary+ skin
- New concept art for all updated skins
- New or edited splash art for all skins
- New Models, VFX and Animations for ALL skins. For Animations, at the very least we have to make a new recall, but in the case of Legendaries or higher we have to do a lot more new animations
- In many cases we also completely rescript the champions kit (if its a old champion)
- Some amount of publishing campaign (varies depending on release)
The skin catalog is really the thing that makes them take 2-3x more then a new Champion, since a new champion only has a launch skin. I don't think people fully understand what goes into remaking a entire skin catalog, especially for a champion with 10+ skins, with legendary tier skins or higher. For old skins we have to sometimes completely re-imagine them, since they might be just a recolor, or not hit modern skin standards.
This is a lot of work, especially given pure ASUs/VUs historically have never increased engagement with a Champion, in the way VGUs do. So at the end of the day the main audience is mains of the Champion, since those are the players most effected by it. Given that, it makes more sense to target higher popularity champs since it will make the largest amount of players happy. At the same time higher popularity champs have larger skin catalogs, so they cost a lot more time/resources to make, so sometime a lower popularity champ can be the same value due to being cheaper to make.
All that said we think it's important and we are always looking at opportunities to do more of these since many of you love them (Myself included)