Which is still less work than creating a brand new skeleton and animations!
You really believe void elves are as much work as a brand new race? How? Most of them don't even have custom dance animations. Most use the same animations as their parent races when it comes to running/walking/sitting.
If you did a checklist of things needed to create your average allied race and compared it to a brand new race, the latter would be longer.
I'm not saying they don't get work done on them - Vulpera tails and sitting animations, Nightborne posture changes, but it's not the same as a new race with new everything. Just logically there is more that goes into a new race.