Because development on various features is done in parallel, it makes sense prioritize cosmetic features that more people will experience in a regular basis... At least in my opinion.
Again, I'm not saying that IVA would not have a positive impact on some players' experience, I'm just guessing, based on my own experience with the game as well as my vicarious experience through others, that IVA has a small impact overall compared to other features, cosmetic or otherwise.