Necrosis relic

The granted skill deals vit dmg, yet its RRs are Aether, Chaos, and Elemental.
If I were using a vit dmg relic like this, vit dmg would definitely take a great portion of the dmg I use. Why can’t make its RR reduce Vit resist?

I also feel that vit dmg builds are poorly supported by equipment when I was trying to build a Vit melee.