Season of Discovery.
Valor Tokens used to be able to be exchanged for Necrotic Runes / Remnants of Valor and now the vendors only give the option for Remnants of Valor. At some point Necrotic Runes were removed as an option for trade, possibly intentional? Have checked all the vendors and all have had the Necrotic Rune option removed. This essentially removes Necrotic Runes main function.