Back during the Mordor heyday, main stats were nerfed from giving 8 points of mastery for each point of might, agility or will.
What this did was make everyone ditch might, agility and will essences in favor of mastery, crit rating and finesse.
Every endgame has been the same way ever since.
Recently with Gundabad, as we needed to be more tanky than usual, we'd still pick mitigation essences over stats.
Might, agility and will do not offer anything sufficient enough to consider slotting them anymore.