There are affix shards for almost every type of damage that can spawn on a melee weapon. These include, but are not limited to, damages such as fire, cold, void, physical, etc.
So my question is why is there not a shard type for melee necrotic damage? I feel like there should be equal representation for all damage types in the affix shards. That way, any build that uses that type of damage could have something to utilize.