Based on the OP's definition of Massive then there hasn't been a proper massive online RPG since EverQuest when you could take a hundred people into a raid. Every other MMO has had party size limitations in the low double-digits.
And the reason why they don't have larger dungeon parties is because it becomes awkward as all hell to design an encounter to actually challenge that many people. When you have no limit to your group size you can steam-roll just about everything without any degree of difficulty.
